Planets Still Forming Detected in a Protoplanetary Disk

An artist rendering of infant star HD 163296 with three protoplanets forming in its disk  The planets were discovered using a new mode of detection — identifying unusual patterns in the flow of gas within a protoplanetary disk. (NRAO/AUI/NSF; S. Dagnello)

Just as the number of planets discovered outside our solar system is large and growing — more than 3,700 confirmed at last count — so too is the number of ingenious ways to find exoplanets ever on the rise.

The first exoplanets were found by measuring the “wobble” in their host stars caused by the gravitational pull of the planets, then came the transit technique that measured dips in the light from stars as planets passed in front of them, followed by the direct imaging of moving objects deemed to be planets, and numerous more.

A new technique can now be added to the toolkit, one that is useful only in specific galactic circumstances but is nonetheless ingenious and intriguing.

By detecting unusual patterns in the flow of gas within the protoplanetary disk of a young star, two teams of astronomers have confirmed the distinct, telltale hallmarks of newly formed planets orbiting the infant star.

In other words, the astronomers found planets in the process of being formed, circling a star very early in its life cycle.

These results came thanks to the Atacama Large Millimeter/submillimeter Array (ALMA), and are presented in a pair of papers appearing in the Astrophysical Journal Letters.

Richard Teague, an astronomer at the University of Michigan and principal author on one of the papers, said that his team looked at “the localized, small-scale motion of gas in a star’s protoplanetary disk. This entirely new approach could uncover some of the youngest planets in our galaxy, all thanks to the high-resolution images coming from ALMA.”

ALMA image of the protoplanetary disk surrounding the young star HD 163296 as seen in dust. ( ALMA: ESO/NAOJ/NRAO; A. Isella; B. Saxton NRAO/AUI/NSF.

To make their respective discoveries, each team analyzed the data from various ALMA observations of the young star HD 163296, which is about 4 million years old and located about 330 light-years from Earth in the direction of the constellation Sagittarius.

Rather than focusing on the dust within the disk, which was clearly imaged in an earlier ALMA observation, the astronomers instead studied the distribution and motion of carbon monoxide (CO) gas throughout the disk.

As explained in a release from the National Radio Astronomy Observatory, which manages the American operations of the multi-national ALMA, molecules of carbon monoxide naturally emit a very distinctive millimeter-wavelength light that ALMA can observe. Subtle changes in the wavelength of this light due to the Doppler effect provide a glimpse into the motion of the gas in the disk.

If there were no planets, gas would move around a star in a very simple, predictable pattern known as Keplerian rotation.

“It would take a relatively massive object, like a planet, to create localized disturbances in this otherwise orderly motion,” said Christophe Pinte of Monash University in Australia and lead author on the other of the two papers. 

And that’s what both teams found.

ALMA is a radio astronomy array located in Chile and set 16,000 feet above sea level. It’s a partnership between the European Southern Observatory (ESO), the National Science Foundation (NSF) of the United States and the National Institutes of Natural Sciences (NINS) of Japan in collaboration with the Republic of Chile. ALMA, which began operations in 2013, is used to observe light from space in comparatively long radio wavelengths. ((ESO/José Francisco Salgado )

Detecting planets within a protoplanetary disk — or finding theorized planets within those disks — is a big deal. 

That’s because information about the characteristics of very young planets orbiting young stars can potentially add substantially to one of the long-debated questions of planetary science:  How exactly did those billions upon billions of planets out there form?

The leading theory of planet formation, the “core accretion model,” has planets forming slowly — with dust, small objects and then planetesimals smashing into a rocky core and leaving matter behind.  In this model, the planet building takes place in a region close to the protoplanet’s stars.

Another theory looks to gravitational instabilities in the disk, arguing that giant planets can form quickly and far from their host stars.

The distribution of current solar system planets and beyond can give some clues based on the size, type and distribution of those planets.  But planets migrate and evolve, and they have never been studied before they had a chance to do much of either.

The techniques currently used for finding exoplanets in fully formed planetary systems — such as measuring the wobble of a star or how a transiting planet dims starlight — don’t lend themselves to detecting protoplanets.

With this new method for looking into those early protoplanetary disks, the hunt for infant planets becomes possible.  And the results in terms of understanding planet formation look to be very promising.

“Though thousands of exoplanets have been discovered in the last few decades, detecting protoplanets is at the frontier of science,” said Pinte.


These earlier images from ALMA reveal details in the planet-forming disk around a nearby sun-like star, TW Hydrae, including an intriguing gap at the same distance from the star as the Earth is from the sun. This structure may mean that an infant version of our home planet is beginning to form there, although these dust gaps are considered to be suggestive rather than conclusive. ( S. Andrews; Harvard-Smithsonian CfA, ALMA (ESO/NAOJ/NRAO)}ALMA

This is not the first time that ALMA images of protoplanetary disks have been used to identify what seem to be protoplanets.

In 2016, a team led by Andrea Isella of Rice University reported the possible detection of two planets, each the size of Saturn, orbiting the same star that is the subject of this week’s report, HD 163296.

These possible planets, which are not yet fully formed, revealed themselves by the dual imprint they left in both the dust and the gas portions of the star’s protoplanetary disk.

But at the time that paper was published, in Physical Review Letters, Isella said the team was focused primarily on the dust in the disks and the gaps they created, and as a result they could not be certain that the features they found were created by a protoplanet.

Teague’s team also studied the dust gaps in the disk of HD 163296, and concluded they provided only  circumstantial evidence of the presence of protoplanets.  What’s more, that kind of detection could not be used to accurately estimate the masses of the planets.

“Since other mechanisms can also produce ringed gaps in a protoplanetary disk,” he said, “it is impossible to say conclusively that planets are there by merely looking at the overall structure of the disk.”

But studying the behavior of the gas allowed for a much greater degree of confidence.


Composite image of the protoplanetary disk surrounding the young star HD 163296. The inner red area shows the dust of the protoplanetary disk. The broader blue disk is the carbon monoxide gas in the system. ALMA observed dips in the concentration and behavior of carbon monoxide in outer portions of the disk, strongly suggesting the presence of planets being formed. ALMA (ESO/NAOJ/NRAO); A. Isella; B. Saxton (NRAO/AUI/NSF)

The team led by Teague identified two distinctive planet-like patterns in the disk, one at approximately 80 astronomical units (AU) from the star and the other at 140 AU. (An astronomical unit is the average distance from the Earth to the sun.)  The other team, led by Pinte, identified the third at about 260 AU from the star. The astronomers calculate that all three planets are similar in mass to Jupiter.

The two teams used variations on the same technique, which looked at anomalies in the flow of the gas – as seen in the shifting wavelengths of the CO emission — that would indicate it was interacting with a massive object.

Teague and his team measured variations in the gas’s velocity. This revealed the impact of several planets on the gas motion nearer to the star.

Pinte and his team more directly measured the gas’s actual velocity, which is better precise method when studying the outer portion of the disk and can more accurately pinpoint the location of a potential planet.

“Although dust plays an important role in planet formation and provides invaluable information, gas accounts for 99 percent of a protoplanetary disks’ mass,” said coauthor Jaehan Bae of the Carnegie Institute for Science.

So while those images of patterns within the concentric rings of a protoplanetary disk are compelling and seem to be telling an important story, it’s actually the gas that is the key.

This is all an important coup for ALMA, which saw its first light in 2013.  The observatory was not designed with protoplanet detection and characterization as a primary goal, but it is now front and center.

Coauthor Til Birnstiel of the University Observatory of Munich said the precision provided by ALMA is “mind boggling.” In a system where gas rotates at about 5 kilometers per second, he said,  ALMA detected velocity changes as small as a few meters per second.

“Oftentimes in science, ideas turn out not to work or assumptions turn out to be wrong,” he said. “This is one of the cases where the results are much more exciting than what I had imagined.


Marc Kaufman
Marc Kaufman is the author of two books about space: "Mars Up Close: Inside the Curiosity Mission” and “First Contact: Scientific Breakthroughs in the Search for Life Beyond Earth.” He is also an experienced journalist, having spent three decades at The Washington Post and The Philadelphia Inquirer. While the “Many Worlds” column is supported and informed by NASA’s Astrobiology Program, any opinions expressed are the author’s alone.

To contact Marc, send an email to

Breakthrough Findings on Mars Organics and Mars Methane

The Curiosity rover on Mars takes a selfie at a site named Mojave. Rock powdered by the rover drill system and then intensively heated rock and then heated to as much as 800 degrees centigrade produced positive findings for long-sought organics. (NASA/JPL-Caltech/MSSS.)

A decades-long quest for incontrovertible and complex Martian organics — the chemical building blocks of life — is over.

After almost six years of searching, drilling and analyzing on Mars, the Curiosity rover team has conclusively detected three types of naturally-occurring organics that had not been identified before on the planet.

The Mars organics Science paper, by NASA’s Jennifer Eigenbrode and much of the rover’s Sample Analysis on Mars (SAM) instrument team, was twinned with another paper describing the discovery of a seasonal pattern to the release of the simple organic gas methane on Mars.

This finding is also a major step forward not only because it provides ground truth for the difficult question of whether significant amounts of methane are in the Martian atmosphere, but equally important it determines that methane concentrations appear to change with the seasons. The implications of that seasonality are intriguing, to say the least.

In an accompanying opinion piece in Science, Inges Loes ten Kate of Utrecht University in  Netherlands wrote of the two papers: “Both these findings are breakthroughs in astrobiology.”

The clear conclusion of these (and other) recent findings is that Mars is not a “dead” planet where little ever changes.  Rather, it’s one with cycles that appear to produce not only methane but also sporadic surface water and changing dune formations.

Remains of 3.5 billion-year old lake that once filled Gale Crater. NASA scientists concluded early in the Curiosity mission that the planet was habitable long ago based on the study of mudstone remains like these. (NASA/JPL-Caltech/MSSS)

Finding organic compounds on Mars has been a prime goal of the Curiosity rover mission.

Those carbon-based compounds surely fall from the sky on Mars, as they do on Earth and everywhere else, but identifying them has proven illusive.

The consequences of that non-discovery have been significant.  Going back to the Viking missions of 1976, scientists concluded that life was not possible on Mars because there were no organics, or none that were detected.

Jen Eigenbrode, research astrobiologist at NASA’s Goddard Space Flight Center. (NASA/W. Hrybyk)

But the reasons for the disappearing organics are pretty well understood.  Without much of an atmosphere to protect it, the Martian surface is bombarded with ultraviolet radiation, which can destroy organic compounds.  Or, in the case of the samples discovered by the SAM team, large organic macromolecules — the likes of proteins, membranes and DNA — are broken up into much smaller pieces.

That’s what the team found, Eigenbrode told me. The organics were probably preserved, she said, because of exceptionally high levels of sulfur present in that part of Gale Crater.

The organics, extracted from mudstone at the Mojave and Confidence Hill sites, had bonded tightly with ancient non-organic material.  The organic material was freed to be collected as gas only after being exposed to temperatures of more than 500 to 800 centigrade in the SAM oven.

“This material was buried for billions of years and then exposed to extreme surface conditions, so there’s a limit to what we can learn about.  Did it come from life?  We don’t know.

“But the fact we found the organic carbon adds to the habitability equation.  It was in a lake environment that we know could have supported life.  Organics are things that organisms can eat.”

It will take different kinds of instruments and samples from drilling deeper into the extreme Martian surface to answer the question of whether the organics came from living microbes.  But for Eigenbrode, future answers of either “yes” or “no” are almost equally interesting.

Finding clear signs of early Martian life would certainly be hugely important, she said.  But a conclusion that Mars never had life — although it had conditions some 3.5 to 3.8 billion years ago quite similar to conditions on Earth at that time — raises the obvious question of “why not?”

NASA’s Curiosity rover raised robotic arm with drill pointed skyward while exploring Vera Rubin Ridge at the base of Mount Sharp inside Gale Crater. This navcam camera mosaic was stitched from raw images taken on Sol 1833, Oct. 2, 2017 and colorized. (NASA/JPL-Caltech/Ken Kremer, Marco Di Lorenzo)

Organic molecules are the building blocks of all known life on Earth, and consist of a wide variety of molecules made primarily of carbon, hydrogen, and oxygen atoms. However, organic molecules can also be made by chemical reactions that don’t involve life.

Examples of non-biological sources include chemical reactions in water at ancient Martian hot springs or delivery of organic material to Mars by interplanetary dust or fragments of asteroids and comets.

It needs to be said that today’s Mars organics announcement was not the first we have heard.  In 2014, a NASA team reported the presence of chlorine-based organics in Sheepbed mudstone at Yellowknife Bay, the first ancient Mars lake visited by Curiosity.

That work, led by NASA Goddard scientists Caroline Freissinet and Daniel Glavin and published in the Journal of Geophysical Research, focused on signatures from unusual organics not seen naturally on Earth.

The organics were complex and made entirely of Martian components, the paper reported.  But because they combined chlorine with the organic hydrocarbons, they are not considered to be as “natural” as the discovery announced today.

And when it comes to organics on Mars, the complicated history of research into the presence of the gas methane (a simple molecule that consists of carbon and hydrogen) also shows the great challenges involved in making these measurements on Mars.

By measuring absorption of light at specific wavelengths, the tunable laser spectrometer on Curiosity measures concentrations of methane, carbon dioxide and water vapor in the Martian atmosphere. (NASA)


The gold-plated Sample Analysis on Mars contains three instruments that make the measurements of organics and methane.  (NASA/Goddard Space Flight Center)

The second Science paper, authored by Chris Webster of NASA’s Jet Propulsion Lab and colleagues, reports that the gas methane has been detected regularly in recent years, with surprising seasonality.

“The history of Mars methane has been frustrating, with reports of some large plumes and spikes detected, but none have been repeatable.  It’s almost like they’re random,” he told me.  “But now we can see a large seasonal cycle in the background of these detections, and that’s extremely important.”

Over three Mars years, or almost five Earth years, Webster said there have been significant increases in methane detected during the summer, and especially the late summer. That tripling of the methane counts is considered too great to be random, especially since the count declines as predicted after the summer ends.

No definite explanation of why this happens has emerged yet, but one theory has been embraced by some scientists.

While it is still cold in the Martian summer, it can get warm enough where the sun shines directly on a collection of ice for some melting to occur.  And that melting, the paper reports, could provide an escape valve for methane collected long ago under the surface.  The process is termed “microseepage.”


This illustration shows the ways in which methane from the subsurface might find its way to the
surface where its release could produce the large seasonal variation in the atmosphere
as observed by Curiosity. Potential methane sources include byproducts from organisms alive or long dead, ultraviolet degradation of organics, or water-rock chemistry; and its losses include atmospheric photochemistry and surface reactions. Seasons refer to the northern hemisphere. The plotted data is from Curiosity’s TLS-SAM instrument, and the curved line through the data is to aid the eye. (NASA/JPL-Caltech)

Methane is a crucial organic in astrobiology because most of that gas found on Earth comes from biology, although various non-biological processes can produce methane as well.

Today’s paper by Webster et al is the third in Science on Mars methane as measured by Curiosity, and it is the first to find a seasonal pattern.  The first paper, in 2013,  actually reported there was no methane measured in early runs, a conclusion that led to push-back from many of those working in the field.

While the Mars methane results released today are being described as a “breakthrough,” they follow closely the findings of a Science paper in 2009 by Michael Mumma and Geronimo Villanueva, both at NASA Goddard.

The two reported then similar findings of plumes of methane on Mars, of a seasonality associated with their distribution, and a similar conclusion that the methane probably was coming from subsurface reservoirs.  Like Webster et al, Mumma and Villanueva said they were unable to determine if the source of methane was biological or geological.

The methane levels in the plumes they found were considerably higher than detected so far by Curiosity, but what they were detecting was quite different.  Using ground-based telescopes, they detected the high concentrations in two specific areas over a number of years, while Curiosity is measuring methane levels that are more global or regional.

Red areas indicate where in 2003 ground-based observers detected concentrations of methane in the Martian atmosphere, measured in parts per billion (ppb).  (NASA / M. Mumma & others)

Just as Webster was criticized for his initial paper saying there was no methane detected on Mars, the Mumma team also got sharp questions about their methodology and conclusions.  This grew as their numerous follow-up efforts to detect the Mars methane proved unsuccessful.

But now Webster says the Curiosity findings have essentially “confirmed” what Mumma and Villanueva reported nine years ago.

Still, the Curiosity results are a breakthrough because they were made on Mars rather than through a telescope. Mumma, who described the new Curiosity results as “satisfying,” agreed that they were a major step forward.

“This is how science works,” he said.  “We do our work and put out our papers and other scientists react.  We take it all in and make changes if needed.  But the big changes come when new, and maybe different, data is presented.”

And that’s exactly what will be happening soon regarding methane on Mars.  Beginning early this year, the European/Russian Trace Gas Orbiter (TGO) has been collecting data specifically on Mars gases including methane.  Unlike previous Mars methane campaigns, this one can potentially determine whether the methane being released from below the surface was formed by biology or geology — although not without great difficulty.

Mumma, who is part of that TGO team, said the first release of information is due in the fall.








Marc Kaufman
Marc Kaufman is the author of two books about space: "Mars Up Close: Inside the Curiosity Mission” and “First Contact: Scientific Breakthroughs in the Search for Life Beyond Earth.” He is also an experienced journalist, having spent three decades at The Washington Post and The Philadelphia Inquirer. While the “Many Worlds” column is supported and informed by NASA’s Astrobiology Program, any opinions expressed are the author’s alone.

To contact Marc, send an email to

Joining the Microscope and the Telescope in the Search for Life Beyond Earth



Niki Parenteau of NASA’s Ames Research Center is a microbiologist working in the field of exoplanet and Mars biosignatures. She adds a laboratory biology approach to a field generally known for its astronomers, astrophysicists and planetary scientists. (Marisa Mayer, Stanford University.)


The world of biology is filled with labs where living creatures are cultured and studied, where the dynamics of life are explored and analyzed to learn about behavior, reproduction, structure, growth and so much more.

In the field of astrobiology, however, you don’t see much lab biology — especially when it comes to the search for life beyond Earth.  The field is now largely focused on understanding the conditions under which life could exist elsewhere, modeling what chemicals would be present in the atmosphere of an exoplanet with life, or how life might begin as an organized organism from a theoretical perspective.

Yes, astrobiology includes and learns from the study of extreme forms of life on Earth, from evolutionary biology, from the research into the origins of life.

But the actual bread and butter of biologists — working with lifeforms in a lab or in the environment — plays a back seat to modeling and simulations that rely on computers rather than actual life.

Niki Parenteau with her custom-designed LED array, can reproduce the spectral features of different simulated stellar and atmospheric conditions to test on primitive microbes. (Marc Kaufman)

There are certainly exceptions, and one of the most interesting is the work of Mary “Niki” Parenteau at NASA’s Ames Research Center in the San Francisco Bay area.

A microbiologist by training, she has been active for over five years now in the field of exoplanet biosignatures — trying to determine what astronomers could and should look for in the search for extraterrestrial life.

Working in her lab with actual live bacteria in laboratory flasks, test tubes and tanks, she is conducting traditional biological experiments that have everything to do with astrobiology.

She takes primitive bacteria known to have existed in some form on the early Earth, and she blasts them with the radiation that would have hit the planet at the time to see under what conditions the organisms can survive.  She has designed ingenious experiments using different forms of ultraviolet light and a LED array that simulate the broad range of radiations that would come from different types of stars as well.

What makes this all so intriguing is that her work uses, and then moves forward, cutting edge modeling from astronomers and astrobiologists regarding thick photochemical hazes understood to have engulfed the early Earth — making the planet significantly colder but also possibly providing some protection from deadly ultraviolet radiation.

That was a time when the atmosphere held very little oxygen, and when many organisms had to make their living via carbon dioxide and sulfur-based photosynthesis that did not use water and did not produce oxygen. This kind of photosynthesis has been the norm for much of the history of life on Earth, and certainly could be common on many exoplanets orbiting other stars as well.

So anything learned about how these early organisms survived in frigid conditions with high ultraviolet radiation — and what potentially detectable byproducts they would have produced under those conditions — would be important in the search for biosignatures and extraterrestrial life.

Parenteau has spent years learning from astronomers working to find ways to characterize exoplanet biosignatures, and she has been eager to convert her own work into something useful to them.

“These are not questions that can be answered by one discipline,” she told me.  “I certainly understand that when it comes to exoplanet biosignatures and life detection, astronomy has to be in the lead.  But biologists have a role to play, especially when it comes to characterizing what life produces.”

When haze built up in the atmosphere of Archean Earth, the young planet might have looked like this artist’s interpretation – a pale orange dot. A team led by Goddard scientists thinks the haze was self-limiting, cooling the surface by about 36 degrees Fahrenheit (20 Kelvins) – not enough to cause runaway glaciation. The team’s modeling suggests that atmospheric haze might be helpful for identifying earthlike exoplanets that could be habitable. (NASA’s Goddard Space Flight Center/Francis Reddy)

Here is the back story to Parenteau’s work:

Recent work by NASA Goddard Space Flight Center astronomer and astrobiologist Giada Arney and colleagues points to the existence of a thick haze around the early Archean Earth and probably today around some, and perhaps many, exoplanets.  This haze — which is more like pollution than clouds — is produced by the interaction of strong incoming radiation and chemicals (most commonly methane and carbon dioxide) already in the atmosphere.

The haze, Arney concluded based on elaborate modeling of those radiation-chemical interactions, would be hard on any life that might exist on the planet because it would reduce surface temperatures significantly, though probably not always fatally.

Giada Arney is an astronomer and astrobiologist at NASA’s Goddard Space Flight Center.  As with Parenteau, her general approach to science was formed at the University of Washington’s pioneering Virtual Planetary Laboratory. (NASA/Goddard Space Flight Center)

On the other hand, the haze would also have the effect of blocking 84 percent of the destructive ultraviolet radiation bombarding the planet — especially the most damaging ultraviolet-C light that would otherwise destroy nucleic acids in cells and disrupt the working of DNA.  (Ultraviolet-C radiation is used as a microbial disinfectant.)

Ozone in our atmosphere now plays the role of blocking the most destructive forms of UV radiation, but ozone is formed from oxygen and on early Earth there was very little oxygen at all.

So how did organisms survive the radiation assault?  Might it have been that haze? And might there be hazes surrounding exoplanets as well?  (None have been found so far.)

It’s difficult enough to sort through the potentially protective role of a haze on early Earth.  To do it for exoplanets requires not only an understanding of the effects of a haze on ultraviolet light, but also how the dynamics of a haze would change based on the amounts and forms of radiation emitted by different types of stars.

It’s all very complicated, but the answers needn’t be theoretical, Arney concluded. They could be tested in a lab.

And that’s where Parenteau comes in, with her desire and ability to design biological experiments that might help scientists understand better how to look for life on distant exoplanets.

“I knew that (Parenteau) had been super interested in this kind of question for a long time,” Arney said.  “She one of the few people in the world with the know-how to simulate an atmosphere, and probably the only one in the world who could do the experiment.”

The 48 LEDs (light-emitting diodes) of the board designed and created by Parenteau and Ames intern Cameron Hearne. Each one is independently controlled and can be used to simulate the amount of radiation arriving on a planetary surface — taking into account the flux from the planet’s star and some aspects of its atmosphere.  A microbe is then exposed to the radiation to see whether or how it can survive. (Niki Parenteau.)

Parenteau’s experiment at first looks pretty low-tech, but in fact it’s very much custom-designed and custom-built.

The ultraviolet bulbs include the powerful, germicidal ultraviolet-C variety, some of the glass for the experiment is made of special quartz that is transparent to that ultraviolet light, the LED array has 48 tiny bulbs that can be controlled by software to provide different amounts and kinds of light as identified and provided by Arney

Before designing and making her own LED board with Ames intern Cameron Hearne, Parenteau met with solar panel specialists who might be able to provide an instrument she could use, but it turned out they were very expensive and not nearly as versatile as she wanted.  Having grown up on a farm in northern Idaho, Parenteau is comfortable with making things from scratch, and her experiments reflect that comfort and talent.

How would Parenteau determine whether the haze does indeed protect the microbial cells after exposing them to the various radiation regimes?  This is how she explained the process, which measures the number of cells living or dead given a simulated UV and stellar bombardment:

“Imagine the cells as soap bubbles in a clear glass.  If you look through the glass, the soap bubbles prevent you from seeing through and the glass has a higher ‘optical density.’ However, if you pop or lyse the soap bubbles, suddenly you can see through the glass and the optical density decreases. 

“The latter represents dead ‘popped’ cells that were killed by the UV irradiation.   I predict that by simulating the spectral qualities of the haze, which decreases the UV flux by 84%, more cells will survive.”

The Parenteau-Arney collaboration is being funded through a National Astrobiology Institute grant to the University of Washington’s famously-interdisciplinary Virtual Planetary Laboratory.

The microbes-and-haze experiment is one of many that Parenteau is working on in the general field of biosignatures.  While the haze experiment is primarily designed to determine if microbes could survive a UV bombardment if a haze was present, she is also working on the central question of what might constitute a biosignature.

With that in mind, she is also measuring the gases produced by microbes under different radiation and atmospheric conditions, and that is directly applicable to searching for extraterrestrial life.

A densely-packed community of microbes, including oxygen-producing cyanobacteria as well as anoxygenic purple and green bacteria, being studied with Parenteau’s LED array. A central question involves what gases are emitted and might be detectable on a distant planet. (Niki Parenteau)


Parenteau’s lab glove box with green, purple and other bacteria that is regularly exposed to radiation conditions believed to have existed on early Earth when a photochemical haze is believed to have been present.  (Marc Kaufman)

If and when she does find particularly interesting results in the gas measurements inside the anaerobic glove box, she says, she knows where to go.

“I would hand the results to an astronomer.  We could say that if a particular kind of exoplanet with a particular atmosphere had microbial life, this is the suite of gases we would expect to be emitted.”

Those gases, Parenteau says, may be photochemically altered as they as they rise through the planet’s atmosphere to the upper levels where they could be detected by the telescopes of the future. But in the challenging and complex world of biosignatures, every bit of hard-won data is most valuable since it could some day lead to a discovery for the ages.



Marc Kaufman
Marc Kaufman is the author of two books about space: "Mars Up Close: Inside the Curiosity Mission” and “First Contact: Scientific Breakthroughs in the Search for Life Beyond Earth.” He is also an experienced journalist, having spent three decades at The Washington Post and The Philadelphia Inquirer. While the “Many Worlds” column is supported and informed by NASA’s Astrobiology Program, any opinions expressed are the author’s alone.

To contact Marc, send an email to

Know Thy Star, Know Thy Planet: How Gaia is Helping Nail Down Planet Sizes


Gaia’s all-sky view of our Milky Way and neighboring galaxies. (ESA/Gaia/DPAC)



(This column was written by my colleague Elizabeth Tasker, now at the Japan Aerospace Exploration Agency (JAXA), Institute of Space and Astronautical Sciences (ISAS).  Trained as an astrophysicist, she researches planet and galaxy formation and also writes on space science topics.  Her book, “The Planet Factory,” came out last year.)


Last month, the European Space Agency’s Gaia mission released the most accurate catalogue to date of positions and motions for a staggering 1.3 billion stars.

Let’s do a few comparisons so we can be suitably amazed. The total number of stars you can see without a telescope is less than 10,000. This includes visible stars in both the northern and southern hemispheres, so looking up on a very dark night will allow you to count only about half this number.

The data just released from Gaia is accurate to 0.04 milli-arcseconds. This is a measurement of the angle on the sky, and corresponds to the width of a human hair at a distance of over 300 miles (500 km.) These results are from 22 months of observations and Gaia will ultimately whittle down the stellar positions to within 0.025 milli-arcseconds, the width of a human hair at nearly 680 miles (1000 km.)

OK, so we are now impressed. But why is knowing the precise location of stars exciting to planet hunters?

The reason is that when we claim to measure the radius or mass of a planet, we are almost always measuring the relative size compared to the star. This is true for all planets discovered via the radial velocity and transit techniques — the most common exoplanet detection methods that account for over 95% of planet discoveries.

It means that if we underestimate the star size, our true planet size may balloon from being a close match to the Earth to a giant the size of Jupiter. If this is true for many observed planets, then all our formation and evolution theories will be a mess.

The size of a star is estimated from its brightness. Brightness depends on distance, as a small, close star can appear as bright as a distant giant. Errors in the precise location of stars therefore make a big mess of exoplanet data.

An artist’s impression of the Gaia spacecraft — which is on a mission to chart a three-dimensional map of our Milky Way. In the process it will expand our understanding of the composition, formation and evolution of the galaxy. (ESA/D. Ducros)

This issue has been playing on the minds of exoplanet hunters.

In 2014, a journal paper authored by Fabienne Bastien from Vanderbilt University suggested that nearly half of the brightest stars observed by the Kepler Space Telescope are not regular stars like our sun, but actually are distant and much larger sub-giant stars. Such an error would mean planets around these stars are 20 – 30% larger than estimated, a particularly hard punch for the exoplanet community as planets around bright stars are prime targets for follow-up studies.

Previous improvements in the accuracy of the measured radii and other properties of stars have already proved their worth. In 2017, a journal paper led by Benjamin Fulton at the University of Hawaii revealed the presence of a gap in the distribution of sizes of super Earths orbiting close to their star. Planets 20% and 140% larger than the Earth appeared to be common, but there was a notable dearth of planets around twice the size of our own.

Super Earth planets with orbits of less than 100 days seem to come in two different sizes. (NASA/Ames/Caltech/University of Hawaii. (B.J.Fulton))

The most popular theory for this gap is that the peaks belong to planets with similar core sizes, but the planets with larger radii have deep atmospheres of hydrogen and helium. This would make the planets belonging to the smaller radii peak true rocky worlds, whereas the second peak would be mini Neptunes: the first evidence of a size distinction between these two regimes.

This split in the small planet population was spotted due to improved measurements of planet radii based on higher precision stellar observations made using the Keck Observatory. With a gap size of only half an Earth-radius, it had previously gone unnoticed due to the uncertainty in planet size measurements.

Both the concern of a significant error in planet sizes and the tantalizing glimpse at the insights that could be achieved with more accurate data is why Gaia is so exciting.

Launched on December 19, 2013, Gaia is a European Space Agency (ESA) space telescope for astrometry; the measurement of the position and motion of stars. The mission has the modest goal of creating a three-dimensional map of our galaxy to unprecedented precision.

Gaia measures the position of stars using a technique known as parallax, which involves looking at an object from different perspectives.

Parallax is easily demonstrated by holding up your finger and looking at it with one eye open and the other closed. Switch eyes, and you will see your finger moves in relation to the background. This movement is because you have viewed your finger from two different locations: the position of your left eye and that of your right.

Parallax is the apparent shift in the position of stars as the Earth orbits the sun. It can be used to determine distances between stars. (ESA/ATG medialab)

The degree of motion depends on the separation between your eyes and the distance to your finger: if you move your finger further from your eyes, its parallax motion will be less. By measuring the separation of your viewing locations and the amount of movement you see, the distance to an object can therefore be calculated.

Since stars are far more distant than a raised finger, we need widely separated viewing locations to detect the parallax. This can be done by observing the sky when the Earth is on opposite sides of its orbit. By measuring how far stars seem to move over a six month interval, we can calculate their distance and precisely estimate their size.

This measurement was first achieved by Friedrich Wilhelm Bessel in 1838, who calculated the distance to the star 61 Cygni. Bessel estimated the star was 10.3 light years from the Earth, just 10% lower than modern measurements which place the star at a distance of 11.4 light years.

However, measuring parallax from Earth can be challenging even with powerful telescopes. The first issue is that our atmosphere distorts light, making it difficult to measure tiny shifts in the position of more distant stars. The second problem is that the measured motion is always relative to other background stars. These more distant stars will also have a parallax motion, albeit smaller than stars closer to Earth.

As a result, the motion measured and hence the distance to a star, will depend on the parallax of the more distant stars in the same field of view. This background parallax varies over the sky, leaving no way on Earth of creating a consistent catalogue of stellar positions.

The Gaia spacecraft’s billion-pixel camera maps stars and other objects in the Milky Way. (C. Carreau/ESA)

These two conundrums are where Gaia has the advantage. Orbiting in space, Gaia simply avoids atmospheric distortion. The second issue of the background stars is tackled by a clever instrument design.

Gaia has two telescopes that point 106.4 degrees apart but project their images onto the same detector. This allows Gaia to see stars from different parts of the sky simultaneously. The telescopes slowly rotate so that each field of view is seen once by each telescope and overlaid with a field 106.4 degrees either clockwise or counter-clockwise to its position. The parallax motion of stars during Gaia’s orbit can therefore be compared both with stars in the same field of view, and with stars in two different directions.

Gaia repeats this across the sky, linking the fields of view together to globally compare stellar positions. This removes the problem of a parallax measurement depending on the motion of stars that just happen to be in the background.

The result is the relative position of all stars with respect to one another, but a reference point is needed to turn this into true distances. For this, Gaia compares the parallax motion to distant quasars.

Quasars are black holes that populate the center of galaxies and are surrounded by immensely luminous discs of gas. Being outside our Milky Way, the distance to quasars is so great that their parallax during the Earth’s orbit is negligibly small. Quasars are too rare to be within the field of view of most stars, but with stellar positions calibrated across the whole sky, Gaia can use any visible quasars to give the absolute distances to the stars.

What did these precisely measured stellar motions do to the properties of the orbiting planets? Did our small worlds vanish or the intriguing division in the sizes of super Earths disappear?

This was bravely investigated in a journal paper this month led by Travis Berger from the University of Hawaii. By matching the stars observed by Kepler to those in the Gaia catalogue, Berger confirmed that the majority of bright stars were indeed sun-like and not the suspected sub-giant population. However, the more precise stellar sizes were slightly larger on average, causing a small shift in the observed small planet radii towards bigger planets.

Planet radii derived from the new Gaia data and the Kepler (DR25) Stellar Properties Catalogue. Red points are confirmed planets while black points are planet candidates. Bottom panel shows the ratio between the two data sets. There is a small shift towards larger planets in the new Gaia data. (Figure 6 in Berger et al, 2018.)

The same result was found in a parallel study led by Fulton, who found a 0.4% increase in planet radii from Gaia compared with the (higher precision than Kepler, but less precision than Gaia) results using Keck.

The papers authored by Berger and Fulton investigated the split in super Earth sizes on short orbits, confirming that the two planet populations was still evident with the high precision Gaia data. Further exploration also revealed interesting new trends.

Fulton noticed that two peaks in the super Earth population appear at slightly larger radii for planets orbiting more massive stars. This is true irrespective of the level radiation the planets are receiving from the star, ruling out the possibility that more massive stars are simply better at evaporating away atmospheres on bigger planets. Instead, this trend implies that bigger stars build bigger planets.

Models proposed by Sheng Jin (Chinese Academy of Sciences) and Christoph Mordasini (the Max Planck Institute for Astronomy) in a paper last year proposed that the location of the split in the super Earth population could be linked to composition.

Planets made of lighter materials such as ices would need a larger size to retain their atmospheres, compared to planet cores of denser rock. If the planet size at the population split marks the transition from large rocky worlds without thick atmospheres to mini-Neptunes enveloped in gas, then it corresponds to the size needed to retain that gas.

Berger suggests that the gap between the planet populations seen in the new Gaia data is best explained by planets with an icy-rich composition. As these planets all have short orbits, this suggests these close-in worlds migrated inwards from a much colder region of the planetary system.

The high precision planet radii measurements from Gaia seem to leave our planet population intact, but suggest new trends worth exploring. This will be a great job for TESS, NASA’s recently launched planet hunter that is preparing to begin its first science run this summer. Gaia’s astrometry catalogue of stars will be ensuring we get the very best from this data.

Marc Kaufman
Marc Kaufman is the author of two books about space: "Mars Up Close: Inside the Curiosity Mission” and “First Contact: Scientific Breakthroughs in the Search for Life Beyond Earth.” He is also an experienced journalist, having spent three decades at The Washington Post and The Philadelphia Inquirer. While the “Many Worlds” column is supported and informed by NASA’s Astrobiology Program, any opinions expressed are the author’s alone.

To contact Marc, send an email to

First Mapping of Interstellar Clouds in Three Dimensions; a Key Breakthrough for Better Understanding Star Formation

This snakelike gas cloud (center dark area) in the constellation Musca resembles a skinny filament. But it’s actually a flat sheet that extends about 20 light-years into space away from Earth, an analysis finds.
(Dylan O’Donnell,

When thinking and talking about “astrobiology,” many people are inclined to think of alien creatures that often look rather like us, but with some kind of switcheroo.  Life, in this view, means something rather like us that just happens to live on another planet and perhaps uses different techniques to stay alive.

But as defined by NASA, and what “astrobiology” is in real scientific terms, is the search for life beyond Earth and the exploration of how life began here.  They may seem like very different subjects but are actually joined at the hip;  having a deeper understanding of how life originated on Earth is surely one of the most important set of clues to how to find it elsewhere.

Those con-joined scientific disciplines — the search for extraterrestrial life and the extraordinarily difficult task of analyzing how it started here — together raise another most complex challenge.

Precisely how far back do we look when trying to understand the origins of life?  Do we look to Darwin’s “warm little pond?” To the Miller-Urey experiment’s conclusion that organic building blocks of life can be formed by sparking some common gases and water with electricity?  To an understanding the nature and evolution of our atmosphere?

The answer is “yes” to all, as well as to scores of additional essential dynamics of our galaxies.  Because to begin to answer those three questions, we also have to know how planets form, the chemical make-up of the cosmos, how different suns effect different exoplanets and so much more.

This is why I was so interested in reading about a breakthrough approach to understanding the shape and nature of interstellar clouds.  Because it is when those clouds of gas and dust collapse under their own gravitational attraction that stars are formed — and, of course, none of the above questions have meaning without preexisting stars.

In theory, the scope of astrobiology could go back further than star-formation, but I take my lead from Mary Voytek, chief scientist for astrobiology at NASA.  The logic of star formation is part of astrobiology, she says, but the innumerable cosmological developments going back to the Big Bang are not.

So by understanding something new about interstellar clouds — in this case determining the 3D structure of such a “cloud” — we are learning about some of the very earliest questions of astrobiology, the process that led over the eons to us and most likely life of some sort on the billions of exoplanets we now know are out there.

Cepheus B, a molecular cloud located in our Milky Galaxy about 2,400 light years from the Earth, provides an excellent model to determine how stars are formed. This composite image of Cepheus B combines data from the Chandra X-ray Observatory and the Spitzer Space Telescope.The Chandra observations allowed the astronomers to pick out young stars within and near Cepheus B, identified by their strong X-ray emission.
Credits X-ray: NASA/CXC/PSU/K. Getman et al.; IRL NASA/JPL-Caltech/CfA/J. Wang et al.

So, what is an interstellar cloud?

It’s the generic name given to an accumulation of gas, plasma, and dust in our and other galaxies, left over from galaxy formation.  So an interstellar cloud is a denser-than-average region of the interstellar medium.

Hydrogen is its primary component, and that hydrogen exists in a wide variety of states depending on the density, the age, the location and more of the cloud.

Until recently the rates of reactions in interstellar clouds were expected to be very slow, with minimal products being produced due to the low temperature and density of the clouds. However, organic molecules were observed in the spectra that scientists would not have expected to find under these conditions, such as formaldehyde, methanol, and vinyl alcohol.

The reactions needed to create such substances are familiar to scientists only at the much higher temperatures and pressures of earth and earth-based laboratories. The fact that they were found indicates that these chemical reactions in interstellar clouds take place faster than suspected, likely in gas-phase reactions unfamiliar to organic chemistry as observed on earth.

What was newly revealed this week is that it is possible to determine the 3D structure of an interstellar cloud. The advance not only reveals the true structure of the molecular cloud Musca, which differs from previous assumptions in looking more like a pancake than a needle.

But the two authors, astrophysicist Konstantinos Tassis of the University of Crete and Aris Tritsis, now a postdoctoral fellow at Australian National University, say their discovery will lead to a better understanding of the evolution of interstellar clouds in general. This, in turn, which will help astronomers answer the longstanding questions of how and why the enormous number and wild variety of stars exists in our galaxy and beyond.

Here is a video put together to help explain the science of Musca and its dimensions.   The work was published in the journal Science, and here is their description of what the video shows:

“The first part of the movie gives an overview of the problem of viewing star-forming clouds in 2D projection. The second part of the video shows the striations in Musca, and the process through which the normal mode spatial frequencies are recovered. The third part of the movie demonstrates how the apparently complex profiles of the intensity cuts through striations are reproduced by progressively summing the theoretically predicted normal modes. At this part of the video (1:30-1:52) the spatial frequencies are scaled to the frequency range of human hearing and are represented by the musical crescendo.”

Credit: Aris Tritsis, Nick Gikopoulos, Valerio Calisse, Kostas Tassis

In an email, Tritsis said that this is the first time that the 3-dimensional coordinates of an interstellar cloud have been measured.

“There have been other crude estimates of the 3D sizes of clouds that relied on many assumptions so this is the first time we were able to determine the size with such accuracy and certainty,” he wrote.

“What we are after is the physics that controls the nature of the stars that will form. This physics will dictate how many star will form and with what masses, but it will also be responsible for shaping the cloud. Thus, this physics is encoded in the shape and that is why we are so interested about it.”

Their pathway in to mapping a 3D cloud was the striations (wispy stripe-like patterns) they detected within the cloud. They show that these striations form by the excitation of fast magnetosonic waves (longitudinal magnetic pressure waves) – the cloud is vibrating, like a bell ringing after it has been struck.

“What we have actually found is that the entire cloud oscillates just like waves on the surface of a pond,” he wrote in his email.

Aris Tritsis, a postdoctoral student at the Australian National University.

“However, in this instance is not the surface of the water that is oscillating but the magnetic field that is threading the cloud. Furthermore, because these waves get trapped, they act like a fingerprint. They are unique and by studying their frequencies we can deduce the sizes of the boundaries that confined them.

“It is the same concept as a violin and a cello making very different sounds. In a similar fashion, clouds with different shapes and sizes will vibrate differently. After having identify the frequencies of these oscillations we scaled them to the frequency range of human hearing to get the ‘song of Musca’!”

By analyzing the frequencies of these waves the authors produce a model of the cloud, showing that Musca is not a long, thin filament as once thought, but rather a vast sheet-like or pancake structure that stretches 20 light-years away from Earth.  (The cloud is some 27 light 490 and 650 light-years from Earth.)

With the determination of its 3D nature, the scientists modeled a cloud that is ten times more spacious than earlier thought.

Konstantinos Tassis of the University of Crete is a star formation specialist. He received his doctorate in theoretical astrophysics at the University of Illinois at Urbana Champaign.

From the 3D reconstruction, the authors were able to determine the cloud’s density. Tritsis and Tassis note that, with its geometry now determined, Musca can be used to test theoretical models of interstellar clouds.

“Because of the fact that Musca is isolated and it is very ordered, it was the obvious choice for us to test our method,” Tritis wrote. “However, other clouds out there could also vibrate globally.

“Knowing the exact dimensions of Musca, we can simulate it in great detail, calculate many different properties of this particular cloud based on different star formation models, and compare them with observations.

“We believe that, with its 3D structure revealed, Musca will now act as a prototype laboratory to study star formation in greater detail than ever before. The Musca star formation saga is only now beginning, and this is a very exciting development that goes beyond this particular discovery.”

And in that way, the discovery is very much a part of the long and broad sweep of astrobiology.


Marc Kaufman
Marc Kaufman is the author of two books about space: "Mars Up Close: Inside the Curiosity Mission” and “First Contact: Scientific Breakthroughs in the Search for Life Beyond Earth.” He is also an experienced journalist, having spent three decades at The Washington Post and The Philadelphia Inquirer. While the “Many Worlds” column is supported and informed by NASA’s Astrobiology Program, any opinions expressed are the author’s alone.

To contact Marc, send an email to