A quick update on a recent column about whether our “golden age” of space science and discovery was in peril because of cost overruns and Trump administration budget priorities that emphasized human space travel over science.
The 2018 omnibus spending bill that was passed Wednesday night by the House of Representatives and Thursday night by the Senate represents a major push back against the administration’s earlier NASA budget proposals. Not only would the agency receive $1.6 billion more funding than proposed by the administration, but numerous projects that had been specifically eliminated in that proposal are back among the living.
They include four Earth science satellites, a lander to accompany the Europa Clipper mission to that potentially habitable moon and, perhaps most important, the Wide Field Infrared Survey Telescope (WFIRST) space telescope.
Funding for that mission, which was the top priority of the space science community and the National Academy of Sciences for the 2020s, was eliminated in the proposed 2019 Trump budget, but WFIRST received $150 million in the just-passed omnibus bill.
A report accompanying the omnibus bill is silent about the proposed cancellation and instructs NASA to provide to Congress in 60 days a cost estimate for the full life cycle of the mission, including any additions that might be needed. So there appears to be a strong congressional desire to see WFIRST launch and operate.
Still hanging fire is the fate of the James Webb Space Telescope, which has fallen behind schedule again and is in danger of crossing the $8 billion cap put into place by Congress in 2011. NASA officials said this week that they will soon announce their determination about whether a breach of the program’s cost cap will occur as a result of further delays.
Four of the five Earth science programs the administration sought to cancel are specifically named for funding in the omnibus bill — the Plankton, Aerosol, Cloud, and ocean Ecosystem (PACE) mission, the CLARREO Pathfinder and Orbiting Carbon Observatory 3 instruments and the Earth observation instruments on the Deep Space Climate Observatory spacecraft. A fifth program was already cancelled by NASA earlier this year for technical reasons.
In all, the Science Mission Directorate would receive $6,221 million, an increase of $456 million. Language in the bill explicitly “reiterates the importance of the decadal survey process and rejects the cancellation of scientific priorities.”
A two-year budget deal reached earlier this year raised spending caps substantially for both defense and non-defense programs, freeing up additional funding that may or may not be available in future years. The 2019 budget needs to be passed in six months, and funds could easily be stripped out then or in subsequent years.
But most important, the administration’s plans to focus on sending astronauts to the moon and establish a colony there could and almost certainly would, in time, eat up large portions of the space science budget.
Under the omnibus bill, NASA would receive $4.79 billion for space exploration efforts, up $466 million over 2017 funding levels. This includes $2.15 million for the heavy-lift Space Launch System and $1.35 for the Orion space capsule.
The bill also provides $350 million to build a second mobile launch platform at the Kennedy Space Center. NASA considered, but did not request, funding in its 2019 proposal for a second platform. If built, it could substantially shorten the gap between the first and second launches of SLS by eliminating the delays that would inevitably come at the launch site as it is modified to handle subsequent larger rockets.
In some of its funding, the omnibus bill seems almost too good to be true.
The planetary science program, for instance, received $300 million more than last year. The $2.2 billion total includes $595 million for work on the Europa Clipper mission and for a follow-on lander — a scientifically exciting aspect of the Europa program, but one that had earlier been cancelled.
The bill also keeps earlier plans to use the SLS to launch Europa Clipper by 2022 and the lander by 2024. An SLS launch would halve the number of years it would take to get the spacecraft to Europa, a moon of Jupiter.
But NASA’s assessment of the SLS program make it highly unlikely that the rockets will be ready for those launches, and there are competing plans to use the second SLS launch to send humans into orbit.
As a kind of added treat, the omnibus bill also provides $23 million for a proposed helicopter NASA has under consideration for the the Mars 2020 rover mission.
The Trump administration has shown great interest in manned missions and little interest in space science and especially Earth science.
Clearly, many members of Congress have very different views, informed no doubt by a highly mobilized space science community. And for now, at least, they appear to have carried the day.
In my recent column about The Northern Lights, the Magnetic Field and Life, I explored the science and the beauty of our planet’s aurora borealis, one of the great natural phenomenon we are most fortunate to see in the far North (and much less frequently in the not-quite-so-far North.)
I learned the hard way that an IPhone camera was really not up to the job; indeed, the battery froze soon after leaving my pocket in the 10 degrees F cold. So the column had few images from where I actually was — about a half hour outside of the Arctic Circle town of Alta.
But here now are some images taken by a generous visitor to the same faraway lodge, who was present the same time as myself.
Her name is Lisa Braithwaite and she is an avid amateur photographer and marketing manager for two popular sites in the English Lake District. This was her first hunting trip for the Northern Lights, and she got lucky. Even in the far northern Norway winter the lights come and go unpredictably — though you can increase your chances if you show up during a time when the sun is actively sending out solar flares.
She came with a Panasonic Lumix DMC-G5 camera and did a lot of research beforehand to increase her chances of capturing the drama should the lights appear. Her ISOs ranged from 1,600 to 64,000, and her shutter speed from 5 to 15 seconds. The aperture setting was 3.5.
In addition to showing some of her work, further on I describe a new NASA-led and international program, based in Norway, to study the still incompletely understood dynamics of what happens when very high energy particles from solar flares meet Earth’s atmosphere.
Partnering with the Japanese Aerospace Exploration Agency (JAXA,) the University of Oslo an other American universities, the two year project will send eleven rockets filled with instruments into the ionosphere to study phenomenon such as the auroral winds and the turbulence that can cause so much trouble to communications networks.
But first, here are some morre of Braithwaite’s images, most taken over a one hour period on a single night.
Vast curtains of light are a common feature, often on the horizon but on good nights high up into the sky. The lights can sometimes shimmer and dance, and can feature what appear to be vast spotlights.
While the grandeur of the lights attracts an ever increasing number of adventurous lovers of natural beauty, NASA is also busy in Norway studying the forces that cause the Aurora Borealis — both for the pure science and to better understand the “space weather” that can effect astronauts in low Earth orbit as well as GPS and other communication signals.
The agency has partnered with Norwegian and Japanese colleagues, and other American scientists, in an effort to generally better understand the Earth’s polar cusp — where the planet’s magnetic field lines bend down into the atmosphere and allow particles from space to intermingle with those of Earthly origin.
Solar flares consist of electrically charged particles. They are attracted by the concentrated magnetic fields in the ionosphere around the Earth’s polar regions. This is the reason why the glorious light shows can be observed pretty much exclusively in the far north or the far south.
The first mission, the Auroral Zone Upwelling Rocket Experiment or AZURE, is scheduled to launch this month. The rocket will take off from Norway’s Andøya Space Center, on an island off the far northwest coast of Norway, about 100 miles southwest of where I was near the town of Alta.
As a NASA release of March 1 described it, AZURE’s instruments will measure the atmospheric density and temperature of the polar atmosphere, and will deploy visible tracers — trimethyl aluminum (TMA) and a barium/strontium mixture, which ionize when exposed to sunlight.
“These mixtures create colorful clouds that allow researchers to track the flow of neutral and charged particles, respectively,” the release reads. “The tracers will be released at altitudes 71 to 155 miles high and pose no hazard to residents in the region.
“By tracking the movement of these colorful clouds via ground-based photography and triangulating their moment-by-moment position in three dimensions, AZURE will provide valuable data on the vertical and horizontal flow of particles in two key regions of the ionosphere over a range of different altitudes.
“Such measurements are critical if we are to truly understand the effects of the mysterious yet beautiful aurora. The results will be key to a better understanding of the effects of auroral forcing on the atmosphere, including how and where the auroral energy is deposited.”
AZURE will focus specifically on measuring the vertical winds in these polar regions, which create a tumultuous particle soup that re-distributes the energy, momentum and chemical constituents of the atmosphere.
AZURE will study the ionosphere, the electrically charged layer of the atmosphere that acts as Earth’s interface to space, focusing specifically on the E and F regions. The E region — so-named by early radio pioneers who discovered that the region was electrically charge, and so could reflect radio waves — lies between 56 to 93 miles above Earth’s surface. The F region resides just above it, between 93 to 310 miles altitude.
The E and F regions contain free electrons that have been ejected from their atoms by the energizing input of the Sun’s rays, a process called photoionization. After nightfall, without the energizing input of the Sun to keep them separated, electrons recombine with the positively charged ions they left behind, lowering the regions’ overall electron density. The daily cycle of ionization and recombination makes the E and F regions especially turbulent and complex.
It has been known for a century that solar flares create the fantastic displays of the Northern and Southern lights. More recently, it has also become well known that solar flares cause problems for both satellites and navigation systems.
Despite decades of study, scientists still lack the basic knowledge required for predicting when such problems will occur. Once they understand this, it should be possible to make good space weather forecasts just like we do with our weather forecasts on Earth.
When solar storms rain down on the Earth, they cause turbulence in the ionosphere. This turbulence is one of the major unsolved problems of classical physics and physicists are hoping that the rockets will lead to a far better understanding of the phenomenon.
“Without such an understanding of turbulence it is impossible to make the calculations needed for being able to predict severe space weather events,” said Joran Moen of the University of Oslo, and one of the project leaders. He spoke with the University of Oslo research magazine “Apollon.”
The rockets of The Grand Challenge Initiative – Cusp mission will launch over the next two years from the Andøya and Svalbard rocket ranges in Norway. Nine of the rockets are from NASA, one from JAXA and one building built the at the University of Norway.
One particular “sounding” will be made with the launch of four rockets at once, an unusual and complex procedure.
Those involved say this will be among the most ambitious attempts ever using rockets for research purposes.
“We will try to launch four of the rockets at the same time. This has never been done before. It is a historic venture,” said Moen.
Yoshifumi Saito of JAXA further explained that “the four parallel rockets are important for us. By using them we can obtain much better scientific results than would have been the case if we had just launched one rocket at a time.”
Important and compelling science. And think of how many times the scientists will be able to experience the glories of the Northern Lights show.
I was moved to weigh in after reading Vice President Mike Pence’s comments last week down at the Kennedy Space Center — a speech that seemed to minimize NASA’s performance in recent years (decades?) and to propose a return to a kind of Manifest Destiny way of thinking in space.
The speech did not appear to bode well for space science, which has dominated NASA news with many years of exploration into the history and working of the cosmos and solar system, the still little-understood domain of exoplanets, the search for life beyond Earth.
Instead, the speech was very much about human space exploration, with an emphasis on “boots on the ground,” national security, and setting up colonies.
“We will beat back any disadvantage that our lack of attention has placed and America will once again lead in space,” Pence said.
“We will return our nation to the moon, we will go to Mars, and we will still go further to places that our children’s children can only imagine. We will maintain a constant presence in low-Earth orbit, and we’ll develop policies that will carry human space exploration across our solar system and ultimately into the vast expanses. As the president has said, ‘Space is,’ in his words, ‘the next great American frontier.’ And like the pioneers that came before us, we will settle that frontier with American leadership, American courage and American ingenuity.” (Transcript here.)
That a new president will have a different kind of vision for NASA than his predecessors is hardly surprising. NASA may play little or no role in a presidential election, but the agency is a kind of treasure trove of high profile possibilities for any incoming administration.
That the Trump administration wants to emphasize human space exploration is also no surprise. Other than flying up and back to construct and use the International Space Station, and then out to the Hubble Space Telescope for repairs, American astronauts have not been in space since the last Apollo mission in 1972. It should be said, however, that no other nation has sent astronauts beyond low Earth orbit, either, since then.
Where I found the speech off-base was to talk down the many extraordinary discoveries in recent decades about our planet, the solar system, the galaxy and beyond made during NASA missions and made possible by cutting-edge NASA technology and innovations.
In fact, many scientists, members of Congress and NASA followers would enthusiastically agree that the last few decades have been an absolute Golden Age in space discovery — all of it done without humans in space (except for those Hubble repairs.)
To argue for a more muscular human space program does not have to come with a diminishing of the enormous space science advances of these more recent years; missions and discoveries that brought to Americans and the world spectacular images and understandings of Mars, of Jupiter and Saturn and their potentially habitable moons, of Pluto, of hot Jupiters, super-Earths and exoplanet habitable zones, and of deep, deep space and time made more comprehensible because of NASA grand observatories.
To say that the United States has given up its “lead in space,” it seems to me, requires a worrisome dismissal of all this and much more.
Let’s start on Mars. For the past 20 years, NASA has had one or more rovers exploring the planet. In all, the agency has successfully landed seven vehicles on the planet — which is the sum total of human machinery that has ever arrived in operational shape on the surface (unless you count the Soviet Mars 3 capsule which landed in 1971 and sent back information for 14 seconds before going silent.)
One of the two rovers now on Mars — Curiosity — has established once and for all time that Mars was entirely habitable in its early life. It has drilled into the planet numerous times and has tested the samples for essential-for-life carbon organic compounds (which it found.) It also has detected clear evidence of long-ago and long-standing lakes and rivers. And it measured radiation levels at the surface over years to help determine how humans might one day survive there.
I think it’s fair to say that Curiosity has advanced an understanding of the history and current realities of Mars more than any other mission, and perhaps more than all the others combined.
Equally important, the almost two-thousand pound rover was delivered to the surface via a new landing technique called the “sky crane.” If your goal is to some day land a human on Mars, then learning how to deliver larger and larger payloads is essential because a capsule for astronauts would weigh something like 80,000 pounds.
The European Space Agency, as well as the Russians and Chinese, have tried to send landers to Mars in recent years, but with no success.
And as for Curiosity, it has been exploring Mars now for almost five years — well past its nominal mission lifetime.
NASA missions to Saturn and Jupiter have sent back images that are startling in their beauty and overflowing in their science. And they have found unexpected features that could some day lead to a discovery of extraterrestrial life in our solar system.
The most surprising discovery was at Saturn’s moon Enceladus, which turns out to be spewing water vapor into space from its south pole region. This water contains, among other important compounds, those organic building blocks of life, as well as evidence that the plumes are generated by hydrothermal heating of the ocean under the surface of the moon.
In other words, there is a global ocean on Enceladus and at the bottom of it water and hot rock are in contact and are reacting in a way that, on Earth at least, would provide an environment suitable for life. And then the moon is spitting out the water to make it quite possible to study that water vapor and whatever might be in it.
If the last decades are a guide, up-close study of these icy moons is a challenge and opportunity that the United States alone — sometimes in collaboration with European partners — has shown the ability and appetite to embrace make happen.
The plumes were investigated and even traversed by the Cassini spacecraft, which is a joint NASA-ESA mission. The primary ESA contribution was the Huygens probe that descended to Titan in 2005. To people in the space science community, these kind of collaborations — generally with European space agencies — allow for more complex missions and good international relations.
Plumes of water vapor have also been tentatively discovered identified on Jupiter’s moon, Europa. The data for the discovery came mostly from the Hubble Space Telescope, and is already a part of the previously approved NASA future. The Europa Clipper is scheduled to launch in the 2020s, to orbit the moon and intensively examine the solar system world believed most likely to contain life.
The plumes would be coming from another large global ocean under a thick shell of ice, a body of water understood to be much older and much bigger than that of Enceladus. Clearly, having some of that H2O available for exploration without going through the thick ice shell would be an enormous obstacle eraser.
A follow-up Europa lander mission has been studied and got favorable reviews from a NASA panel, but was not funded by the Trump Administration. Several follow-up Enceladus life-detection missions are currently under review.
I think one could make a strong case that the Hubble Space Telescope has been the most transformative, productive and admired piece of space technology ever made.
For more than two decades now it has been the workhorse of the astrophysics, cosmology and exoplanet communities, and has arguably produced more world-class stunning images than Picasso. In terms of exploring the cosmos and illustrating some of what’s out there, it has no competition.
There is little point to describing its specific accomplishments in terms of discovery because they are so many. Suffice it to say that a collection of published science papers using Hubble data would be very, very thick.
And because of past NASA, White House and congressional commitment to space science, the over-budget and long behind-schedule James Webb Space Telescope is now on target to launch late next year. The Webb will potentially be as revelatory as the Hubble, or even more so in terms of understanding the early era of the universe, the nature and origin of ubiquitous dark matter, and the composition of exoplanets.
Preliminary planning for the great observatory for the 2030s is underway now, and nobody knows whether funding for something as ambitious will be available.
Many of the early exoplanet discoveries were made by astrophysicists at ground-based observatories, and were made by both American, European and Canadian scientists. NASA’s Spitzer Space Telescope and others played a kind of supporting role for the agency, but that all changed with the launch of NASA’s Kepler Space Telescope.
From 2009 to today, the Kepler has identified more than 4,000 exoplanet candidates with more than 2,400 confirmed planets, many of which are rocky like Earth. Of roughly 50 near-Earth size habitable zone candidates detected by Kepler, more than 30 have been verified.
The census provided by Kepler, which looked fixedly at only one small part of the deep sky for four years until mechanical, led to the consensus conclusion that the Milky Way alone is home to billions of planets and that many of them are rocky and in the habitable zone of their host stars.
In other words, Kepler made enormous progress in defining the population of exoplanets likely to exist out there — a wild menagerie of objects very different from what might have been expected, and in systems very different as well.
Two additional NASA observatories designed to detect and study exoplanets are scheduled to launch in the next decade.
Given the number of references to our moon in Pence’s Kennedy Space Station speech — and the enormous costs of the also often referenced humans-to-Mars idea — my bet is that moon landings and perhaps a “colony” will be the Administration’s human space exploration project of choice.
I say this because it is achievable, with NASA rockets and capsules under construction and the fast-growing capabilities of commercial space competitors. We have, after all, proven that astronauts can land and survive on the moon, and a return there would be much less expensive than sending a human to Mars and back. (I’m also skeptical that such a trip to Mars will be technically feasible any time in the foreseeable future, though I know that others strongly disagree.)
As readers of Many Worlds may remember, I’m a fan of a human spaceflight project championed by former astronaut and head of NASA’s Science Directorate John Grunsfeld to assemble a huge observatory in space designed to seriously look for life around distant stars. This plan is innovative, would give NASA and astronauts an opportunity learn how to live and work in deep space, and would provide another science gem. It would indeed show American space leadership.
But here is why I think a moon colony is going to be the choice: Russia, China and the Europeans have all announced tentative plans to build moon colonies in the next decade or two. So for primarily strategic, competitive and national security reasons, it seems likely that this kind of “new frontier” is what the administration has in mind.
After all, Pence also said in his speech at the KSC that “Under President Donald Trump, American security will be as dominant in the heavens as we are here on Earth.” (An apparent reference to both NASA and the military space program, which is significantly better funded than NASA.)
Setting up an American moon colony would be very costly in dollars, time and focus, but it’s not necessarily a bad thing. Given that a pie can be sliced just so many ways, however, it’s pretty clear that a major moon colony project would end up taking a significant amount of funding away from space science missions.
Returning to the moon and even setting up a colony is not, however, an example of American leadership. Rather, it would constitute a decision for the United States and NASA to, in effect, follow the pack.
The Many Worlds site has been down for almost two weeks following the crash of the server used to publish it. We never expected it would take quite this long to return to service, but now we are back with a column today and another one for early next week.
Earth is most fortunate to have vast webs of magnetic fields surrounding it. Without them, much of our atmosphere would have been gradually torn away by powerful solar winds long ago, making it unlikely that anything like us would be here.
Scientists know that Mars once supported prominent magnetic fields as well, most likely in the early period of its history when the planet was consequently warmer and much wetter. Very little of them is left, and the planet is frigid and desiccated.
These understandings lead to an interesting question: if Mars had a functioning magnetosphere to protect it from those solar winds, could it once again develop a thicker atmosphere, warmer climate and liquid surface water?
James Green, director of NASA’s Planetary Science Division, thinks it could. And perhaps with our help, such changes could occur within a human, rather than an astronomical, time frame.
In a talk at the NASA Planetary Science Vision 2050 Workshop at the agency’s headquarters, Green presented simulations, models, and early thinking about how a Martian magnetic field might be re-constituted and the how the climate on Mars could then become more friendly for human exploration and perhaps communities.
It consisted of creating a “magnetic shield” to protect the planet from those high-energy solar particles. The shield structure would consist of a large dipole—a closed electric circuit powerful enough to generate an artificial magnetic field.
Simulations showed that a shield of this sort would leave Mars in the relatively protected magnetotail of the magnetic field created by the object. A potential result: an end to largescale stripping of the Martian atmosphere by the solar wind, and a significant change in climate.
“The solar sytstem is ours, let’s take it,” Green told the workshop. “And that, of course, includes Mars. But for humans to be able to explore Mars, together with us doing science, we need a better environment.”
Is this “terraforming,” the process by which humans make Mars more suitable for human habitation? That’s an intriguing but controversial idea that has been around for decades, and Green was wary of embracing it fully.
“My understanding of terraforming is the deliberate addition, by humans, of directly adding gases to the atmosphere on a planetary scale,” he wrote in an email.
“I may be splitting hairs here, but nothing is introduced to the atmosphere in my simulations that Mars doesn’t create itself. In effect, this concept simply accelerates a natural process that would most likely occur over a much longer period of time.”
What he is referring to here is that many experts believe Mars will be a lot warmer in the future, and will have a much thicker atmosphere, whatever humans do. On its own, however, the process will take a very long time.
To explain further, first a little Mars history.
Long ago, more than 3.5 billion years in the past, Mars had a much thicker atmosphere that kept the surface temperatures moderate enough to allow for substantial amounts of surface water to flow, pool and perhaps even form an ocean. (And who knows, maybe even for life to begin.)
But since the magnetic field of Mars fell apart after its iron inner core was somehow undone, about 90 percent of the Martian atmosphere was stripped away by charged particles in that solar wind, which can reach speeds of 250 to 750 kilometers per second.
Mars, of course, is frigid and dry now, but Green said the dynamics of the solar system point to a time when the planet will warm up again.
He said that scientists expect the gradually increasing heat of the sun will warm the planet sufficiently to release the covering of frozen carbon dioxide at the north pole, will start water ice to flow, and will in time create something of a greenhouse atmosphere. But the process is expected to take some 700 millon years.
“The key to my idea is that we now know that Mars lost its magnetic field long ago, the solar wind has been stripping off the atmosphere (in particular the oxygen) ever since, and the solar wind is in some kind of equilibrium with the outgassing at Mars,” Green said. (Outgassing is the release of gaseous compounds from beneath the planet’s surface.)
“If we significantly reduce the stripping, a new, higher pressure atmosphere will evolve over time. The increase in pressure causes an increase in temperature. We have not calculated exactly what the new equilibrium will be and how long it will take.”
The reason why is that Green and his colleagues found that they needed to add some additional physics to the atmospheric model, dynamics that will become more important and clear over time. But he is confident those physics will be developed.
He also said that the European Space Agency’s Trace Gas Orbiter now circling Mars should be able to identify molecules and compounds that could play a significant role in a changing Mars atmosphere.
So based on those new magnetic field models and projections about the future climate of Mars, when might it be sufficiently changed to become significantly more human friendly?
Well, a relatively small change in atmospheric pressure can stop an astronaut’s blood from boiling, and so protective suits and clothes would be simpler to design. But the average daily range in temperature on Mars now is 170 degrees F, and it will take some substantial atmospheric modification to make that more congenial.
Green’s workshop focused on what might be possible in the mid 21st century, so he hopes for some progress in this arena by then.
One of many intriguing aspects of the paper is its part in an NASA effort to link fundamental models together for everything from predicting global climate to space weather on Mars.
The modeling of a potential artificial magnetosphere for Mars relied, for instance, on work done by NASA heliophysics – the quite advanced study of our own sun.
Chuanfei Dong, an expert on space weather at Mars, is a co-author on the paper and did much of the modeling work. He is now a postdoc at Princeton University, where he is supported by NASA.
He used the Block-Adaptive-Tree Solar-Wind Roe-Type Upwind Scheme (BATS-R-US) model to test the potential shielding effect of an artificial magnetosphere, and found that it was substantial when the magnetic field created was sufficiently strong. Substantial enough, in fact, to greatly limit the loss of Martian atmosphere due to the solar wind.
As he explained, the artificial dipole magnetic field has to rotate to prevent the dayside reconnection, which in turn prevents the nightside reconnection as well.
If the artificial magnetic field does not block the solar winds properly, Mars could lose more of its atmosphere. That why the planet needs to be safely within the magnetotail of the artificial magnetosphere.
In their paper, the authors acknowledge that the plan for an artificial Martian magnetosphere may sound “fanciful,” but they say that emerging research is starting to show that a miniature magnetsphere can be used to protect humans and spacecraft.
In the future, they say, it is quite possible that an inflatable structure can generate a magnetic dipole field at a level of perhaps 1 or 2 Tesla (a unit that measures the strength of a magnetic field) as an active shield against the solar wind. In the simulation, the magnetic field is about 1.6 times strong than that of Earth.
As a summary of what Green and others are thinking, here is the “results” section of the short paper:
“It has been determined that an average change in the temperature of Mars of about 4 degrees C will provide enough temperature to melt the CO2 veneer over the northern polar cap.
“The resulting enhancement in the atmosphere of this CO2, a greenhouse gas, will begin the process of melting the water that is trapped in the northern polar cap of Mars. It has been estimated that nearly 1/7th of the ancient ocean of Mars is trapped in the frozen polar cap. Mars may once again become a more Earth-like habitable environment.
The results of these simulations will be reviewed (with) a projection of how long it may take for Mars to become an exciting new planet to study and to live on.”
Seven years ago this month the Kepler spacecraft launched into space – the first NASA mission dedicated to searching for planets around distant stars. The goal was to conduct a census of these exoplanets, to learn whether planets are common or rare. And in particular, to understand whether planets like Earth are common or rare.
With the discovery and confirmation of over 1,000 exoplanets (and thousands more exoplanet candidates that have not yet been confirmed), Kepler has taught us that planets are indeed common, and scientists have been able to make new inferences about how planetary systems form and evolve. But the planets found by Kepler are almost exclusively around distant, faint stars, and the observations needed to further study and characterize these planets are challenging. Enter TESS.
The Transiting Exoplanet Survey Satellite (TESS) is a NASA Explorer mission designed to search for new exoplanets around bright, nearby stars. The method that TESS will use is identical to that used by Kepler – it looks for planets that transit in front of their host star. Imagine that you’re looking at a star, and that star has planets around it.
If the orbit of the planet is aligned correctly, then once per “year” of the planet (i.e. once per orbit), the planet will pass in front of the star. As the planet moves in front of the star, it blocks a small fraction of the light, so the star appears to get slightly fainter. As the planet moves out of transit, the star returns to normal brightness. We can see an example of this in our own solar system on May 9, 2016, as Mercury passes in front of the Sun.
We can learn a lot from observing the transits of a planet. First, we can learn the size of a planet – the bigger the planet, the more light it will block, and the larger the “dip” in the brightness of the host star. Second, we can learn how long the planet’s year is – since it only passes in front of the star once per orbit, the time between transits is the planet’s year.
The duration of the year, in combination with the properties of the host star, also allows us to determine if a planet might be habitable. With high precision measurements, we can also infer much more about the orbit of the planet (e.g., the eccentricity of the orbit). And, in fact, in some cases, we can look at small changes in the apparent year of the planet to discover additional planets in the system that do not transit (Transit Timing Variations).
To observe these transits, TESS will use four identical, extremely precise cameras mounted behind four identical 8-inch telescopes. Each one of these cameras will be sensitive to changes in the brightness of a star as small as about 40 parts per million, allowing TESS to detect planets even smaller than our planet.
Earth, transiting the sun, would produce a dip of about 100 parts per million. Each of the four cameras has a field-of-view of 24°×24°, and the fields of the four cameras are adjacent so that TESS will instantaneously observe a 24°×96° swath of the sky (referred to as an observation sector). Within this field, TESS will collect “postage stamp” images of about 8,000 stars every two minutes – the postage stamps are small sub-images, nominally about 10×10 pixels.
TESS will stare continuously at each of these observation sectors for 27 days before moving to the next sector; over the course of one year, this will give TESS coverage of almost one entire hemisphere, with postage stamp data on approximately 100,000 stars. In the second year of the TESS mission, 13 additional sectors will cover the other hemisphere of the sky, resulting in observations of about 200,000 stars.
The method used for these postage stamp-sized observations is very similar to that used for Kepler, but the survey itself is different. While TESS is conducting an all-sky survey (about 40,000 square degrees), Kepler looked at only a relatively small patch of the sky (115 square degrees). But with a telescope seven times larger than those on TESS, Kepler was able to look much further away – TESS surveys stars within only about 200 light years, compared to 3,000 light years for Kepler.
This underscores the difference in the underlying philosophy of the two missions. The goal of Kepler was to understand the statistics of exoplanets, to conduct a census to understand the population as a whole.
TESS, on the other hand, is about finding planets around bright, nearby stars –planets that will be well-suited to follow-up observations from both the ground and from space. On average, the stars observed by TESS will be between 30 and 100 times brighter than those observed by Kepler. These brighter targets will allow for follow-up observations that will be critical for understanding the nature of the newly discovered planets – more on that in a moment.
In raw numbers, what do we expect from TESS?
Former MIT graduate student Peter Sullivan conducted detailed simulations of the mission to make a prediction on what it might discover, and these results are incredible. With TESS, we expect to find over 1,600 new exoplanets within the postage stamp data, with about 70 of those being about the size of the Earth (within 25% of the Earth’s diameter), and almost 500 “super-Earth” planets (less than twice the diameter of Earth).
Perhaps most exciting is the likelihood that TESS will discover a handful of Earth-sized planets in the habitable zones of their host stars.
In addition, while TESS obtains the postage stamp data every two minutes, it also obtains a full-frame image – a picture of the entire observing sector – every thirty minutes.
In those data, we expect to find over 20,000 additional planets. The majority of those will be large (Jupiter-size) planets, but there will also be about 1,400 additional super-Earths discovered. The sheer number of planets that will be found is amazing, but more important than the number is the fact that all of these planets will be orbiting bright, nearby stars. This is a fantastic leap relative to where we were just 25 years ago, when not a single exoplanet was known.
One of the challenges of transit measurements is that they can produce false positives. Stellar activity can cause quasi-periodic dips in the brightness of a star. An eclipsing binary star in the background could mimic the dip from a transiting planet. With careful analysis, most of these effects can be accounted for, but it remains important to follow a transit observation with a confirmation — making a secondary measurement to ensure that what was observed is, in fact, a planet.
The most straightforward way to confirm a transiting exoplanet is with a radial velocity (RV) measurement. The RV method takes advantage of the reflex motion of the star; as a planet orbits a star, the star itself doesn’t remain stationary. In fact, both the planet and the star orbit the center of mass of the system. So, if one looks at spectral lines from the host star, it is possible to measure the Doppler shift of those lines as the star does it’s little pirouette around the center of mass.
From this data, astronomers can measure the mass and the year (orbital period) of the exoplanet. This confirms the orbital period observed from the transit data, and the combination of radius (observed from the transit) and the mass (observed from the RV) gives us the bulk density of the planet. With that, we can make inferences about the composition of the planet – is it a rock, like Earth? A water-world or a ball of ice? A gas giant?
Making the RV measurement, while straightforward, is not an easy one – less than 10% of the exoplanet candidates found by Kepler have been confirmed with RV measurements, largely because the host stars themselves are faint. For TESS, however, because the host stars are nearby and bright, it will be possible to make follow-up observations on nearly all of the stars that host small planets – the only major limitation will be due to the noise from the stars themselves (i.e. flares, starspots).
Further, because these host stars are bright, they will also be excellent targets for transit spectroscopy. Imagine, for a moment, that there is a transiting planet with a very large atmosphere, and that this atmosphere is transparent in red and blue, but completely opaque in the green. Then, if you observe the planet in red light (or blue light), only the “rock” part of the planet will block light from the star. In green light, however, the rock and the atmosphere will both block light – in the green, the planet appears to be larger than at other wavelengths.
This is the core idea behind transit spectroscopy. By measuring how the apparent size of a transiting planet varies with wavelength, we can infer the composition (and potentially the structure) of the planetary atmosphere. This technique has been used successfully on a very small number of exoplanets to date, but with the large number of planets that TESS will find, and the fact that they will all be around bright, nearby stars, it will be possible to use the James Webb Space Telescope and the next generation of large ground-based telescopes to make these observations.
For the first time, astronomers will actually be able to study not only individual exoplanets, but will be able to study enough of them to make comparisons and draw conclusions about how planets form and evolve.
For me, TESS is endlessly exciting. The sheer quantity of new exoplanets is stunning. The ability to use follow-up observations to characterize these planets will create new paths for scientific investigation. And the discoveries made will help define the science that will be pursued by future missions such as WFIRST, and perhaps more ambitious missions in the future. But, perhaps most exciting, TESS is in part about making “Exoplanets for Everyone.”
In a few years, it will be possible for everyone to go outside to a dark location, point at a star that you can see with the naked eye, and say “there is a planet around that star.” And the night sky may never feel quite the same again.
This blog is being hosted by Knowinnovation Inc. and is supported by the Lunar and Planetary Institute (LPI). LPI is operated by the Universities Space Research Association (USRA) under a cooperative agreement with NASA. The purpose of this blog is to communicate the work of the Nexus for Exoplanet Systems Science (NExSS). Any opinions, findings, and conclusions or recommendations expressed on this blog or its comments are those of the author(s) and do not necessarily reflect the views of NASA.