A pair of astronomers combing through data from the Kepler spacecraft have discovered the first exomoon. The moon is in the Kepler 1625 system about 8,000 light years away, in the constellation Cygnus. It orbits the gas giant Kepler 1625b, and, unlike all the moons in our Solar System, this one is a “gas moon.”
It was only a matter of time before we found an exomoon. We’ve found thousands of exoplanets, thanks mostly to the Kepler spacecraft. And where there are planets, we can expect moons. But even though it seemed inevitable, the first confirmed exomoon is still exciting.
At 6:51 EDT on Wednesday, April 18th, a SpaceX Falcon 9 rocket blasted off from Florida’s Cape Canaveral. It was carrying NASA’s TESS: the Transiting Exoplanet Survey Satellite. From what we can tell, the mission went without a hitch, with the first stage returning to land on its floating barge in the Atlantic Ocean, and stage 2 carrying on to send TESS into its final orbit.
This is a changing of the guard, as we’re now entering the final days for NASA’s Kepler Space Telescope. It’s running out of fuel and already crippled by the loss of its reaction wheels. In just a few months NASA will shut it down for good.
That is sad, but don’t worry, with TESS on its way, the exoplanet science journey continues: searching for Earth-sized worlds in the Milky Way.
It’s hard to believe that we’ve only known about planets orbiting other stars for just over 20 years now. The first extrasolar planet found was the hot jupiter 51 Pegasi B, which was discovered in 1995 by a team of Swiss astronomers.
They found this world using the radial velocity method, where the gravity of the planet pulls its star back and forth, changing the wavelength of the light we see ever so slightly. This technique has been refined and used discover many more planets orbiting many more stars.
But another technique has been even more successful: the transit technique. This is where the light from the star is carefully measured over time, watching for any dip in brightness as a planet passes in front.
At the time that I’m writing this article in April, 2018, there are 3,708 confirmed planets with several thousand more candidates that need additional confirmation.
Planets are everywhere, in all shapes and sizes. From the familiar gas giants, rocky worlds and ice giants we have in the Solar System, to the unusual hot jupiters and super earths. Astronomers have even found comets in other solar systems, planets like Saturn but with ring systems that dwarf our neighbouring planet. The hunt is even on for exomoons. Moons orbiting planets orbiting other stars.
NASA’s Kepler Space Telescope was the most productive planet hunting instrument ever built. Of those 3,708 planets discovered so far, Kepler turned up 2,342 worlds.
Kepler was launched back in March 2009, and began operations on May 12, 2009. It used its 1.4 meter primary mirror to observe a 12-degree region of the sky. Just for comparison, the Moon takes up about half a degree. So a region containing hundreds of times the size of the Moon.
Kepler was placed into an Earth-trailing orbit around the Sun, with a period of 372.5 days. With a longer year, the telescope slowly drifts behind the Earth by about 25 million km per year.
As I mentioned earlier, Kepler was designed to use the transit technique, searching for planets passing in front of their stars in this very specific region of the sky. While previous exoplanet surveys had only found the more massive planets, Kepler was sensitive enough to see worlds with half the mass of Earth orbiting other stars.
And everything was going great until July 14, 2012 when one of the spacecraft’s four reaction wheels failed. These are gyroscopes that allow the spacecraft to change its orientation without propellant. No problem, Kepler was designed to only need three. Then a second wheel failed on May 11, 2013, bringing an end to its main mission.
What the Kepler engineers came up with is one of the most ingenious spacecraft rescues in the history of spaceflight. They realized that they could use light pressure from the Sun to perfectly stabilize the telescope and keep it pointed at a region of the sky.
This allowed Kepler to keep working, observing even larger portions of the sky, but its orbit around the Sun would only let it watch one region for a shorter period of time. Instead of scanning Sun-like stars, Kepler focused its attention on red dwarf stars, which can have Earth sized worlds orbiting them every few days.
This was known as the K2 era, and during this time it turned up an additional 307 confirmed, and 480 unconfirmed planets.
But Kepler is running out of time now. About a month ago NASA announced that Kepler’s almost out of fuel. This fuel is important because one important maneuver it needs to make is to point itself back and Earth and upload all the data it’s been gathering. NASA figures that’s just a few months away now, and when it happens, they’ll instruct the telescope to point at Earth for one last time, transmit its final data, and then shut down forever.
And today TESS blasted off successfully, making its way to take over where Kepler leaves off.
The TESS mission has been around in some form since 2006 when it was originally conceived as a privately funded mission by Google, the Kavli Foundation and MIT.
Over the years, it was proposed to NASA, and in 2013, it was accepted as one of NASA’s Explorer Missions. These are missions with a budget of $200 million or less. WISE and WMAP are other examples of Explorer Missions.
But there are a bunch of differences between Kepler and TESS.
It’ll be capable of surveying the entire sky over the course of two years, which is an area 400 times larger than Kepler observed. And astronomers are expecting that the mission will turn up thousands of extrasolar planets, 500 of which will be Earth-sized or super-Earth-sized.
By performing this wide survey of the sky with bright stars, TESS will be finding the close extrasolar planets. If a bright star has planets passing in front of it from our perspective, TESS will find it. It will create the definitive catalog of nearby planets.
Since these worlds are much brighter in the sky, it’ll be easier for the world’s ground and space-based observatories to do follow up observations. Astronomers will be able to measure the size, mass, density and even the atmospheres of extrasolar worlds. Just wait until James Webb gets its detectors on some of these worlds.
In addition to its primary job of finding planets, NASA has invited Guest Investigators to use the spacecraft for other science research, such as finding quasars, tracking stellar rotation, and observing the variations of dwarf stars. Anything that has a change in brightness will a great target for TESS.
One interesting feature of the TESS mission will be its orbit, taking it on a path that no other mission has ever used. It’s called a “P/2 lunar-resonant” orbit, and takes the spacecraft on an elliptical trajectory that takes half as long as the Moon to orbits the Earth – 13.7 days.
At its closest point to Earth, it’ll be 35,785 km above the surface and take three hours to transmit all its data to ground stations. Then it’ll fly out to the highest point, at an altitude of 373,300 km, out of the hazards of the Van Allen Belts.
By the time the TESS mission wraps up, we’re going to know a lot about the extrasolar planets in our nearby neighborhood. Well, a lot about the planets that perfectly line up with their stars from our perspective. And sadly, this is only a couple of percent of the star systems out there.
We’re going to need other techniques to find the rest, which I’m sure we’ll be covering in future articles.
As of March 1st, 2018, 3,741 exoplanets have been confirmed in 2,794 systems, with 622 systems having more than one planet. Most of the credit for these discoveries goes to the Kepler space telescope, which has discovered roughly 3500 planets and 4500 planetary candidates. In the wake of all these discoveries, the focus has shifted from pure discovery to research and characterization.
In this respect, planets detected using the Transit Method are especially valuable since they allow for the study of these planets in detail. For example, a team of astronomers recently discovered three Super-Earths orbiting a star known GJ 9827, which is located just 100 light years (30 parsecs) from Earth. The proximity of the star, and the fact that it is orbited by multiple Super-Earths, makes this system ideal for detailed exoplanet studies.
As with all Kepler discoveries, these planets were discovered using the Transit Method (aka. Transit Photometry), where stars are monitored for periodic dips of brightness. These dips are the result of exoplanets passing in front of the star (i.e. transiting) relative to the observer. While this method is ideal for placing constraints on the size and orbital periods of a planet, it can also allow for exoplanet characterization.
Basically, scientists are able to learn things about their atmospheres by measuring the spectra produced by the star’s light as it passes through the planet’s atmosphere. Combined with radial velocity measurements of the star, scientists can also place constraints on the planet’s mass and radius and can determine things about the planet’s interior structure.
For the sake of their study, the team analyzed data obtained by the K2 mission, which showed the presence of three Super-Earths around the star GJ 9827 (GJ 9827 b, c, and d). Since they initially submitted their research paper back in September of 2017, the presence of these planets has been confirmed by another team of astronomers. As Dr. Rodriguez told Universe Today via email:
“We detected three super-Earth sized planets orbiting in a very compact configuration. Specifically, the three planets have radii of 1.6, 1.2, and 2.1 times the radius of Earth and all orbit their host star within 6.2 days. We note that this system was independently discovered (simultaneously) by another team from Wesleyan University (Niraula et al. 2017).”
These three exoplanets are especially interesting because the larger of the two have radii that place them in the range between being rocky or gaseous. Few such exoplanets have been discovered so far, which makes these three a prime target for research. As Dr. Rodriguez explained:
“Super Earth sized planets are the most common type of planet we know of but we do not have one in our own solar system, limiting our ability to understand them. They are especially important because their radii span the rock to gas transition (as I discuss below in one of the other responses). Essentially, planets larger then 1.6 times the radius of the Earth are less dense and have thick hydrogen/helium atmospheres while planets smaller are very dense with little to no atmosphere.”
Another interesting thing about these super-Earths is how their short orbital periods – which are 1.2, 3.6 and 6.2 days, respectively – would result in fairly hot temperatures. In short, the team estimates that the three super-Earths experience surface temperatures of 1172 K (899 °C; 1650 °F), 811 K (538 °C; 1000 °F), and 680 K (407 °C; 764 °F), respectively.
By comparison, Venus – the hottest planet in the Solar System – experiences surface temperatures of 735 K (462 °C; 863 °F). So while temperatures on Venus are hot enough to melt lead, conditions on GJ 9827 b are almost hot enough to melt bronze.
However, the most significant thing about this discovery is the opportunities it could provide for exoplanet characterization. At just 100 light-years from Earth, it will be relatively easy for the next-generation telescopes (such as the James Webb Space Telescope) to conduct studies of their atmospheres and provide a more detailed picture of this system of planets.
In addition, these three strange planets are all in the same system, which makes conducting observation campaigns that much easier. As Rodriguez concluded:
“The GJ 9827 system is unique because one planet is smaller than this cutoff, one planet is larger, and the third planet has a radius of ~1.6 times the radius of the Earth, right on that border. So in one system, we have planets that span this rock to gas transition. This is important because we can study the atmosphere’s of these planets, look for differences in the composition of their atmospheres and begin to understand why this transition occurs at 1.6 times the radius of the Earth. Since all three planets orbit the same star, the effect of the host star is kept constant in this “experiment”. Therefore, if these three planets in GJ 9827 were instead orbiting three separate stars, we would have to worry about how the host star is influencing or affecting the planet’s atmosphere. In the GJ 9827 system, we do not have to worry about this since they orbit the same star.”
The discovery of alien life is one of those things that everyone thinks about at some point. Hollywood has made their version of first contact very clear: huge alien vessels appear over Earth’s cities, panic ensues, and Will Smith saves the day with a Windows 3.1 virus. It’s lots of fun—and who knows?—it may end up being accurate. (Not the Windows 3.1 part.) But sci-fi books and movies aside, what do we really know about our attitude to the discovery of alien life?
We have an organization (SETI) dedicated to detecting the presence of alien civilizations, and we have a prominent scientist (Stephen Hawking) warning against advertising our own presence. Those represent the extremes—actively seeking out alien life vs. hiding from it—but what is the collective attitude towards the discovery of alien life? Scientists at Arizona State University (ASU) have studied that issue and detailed their results in a new study published in the journal Frontiers of Psychology.
The team of scientists tried to gauge people’s reactions to the discovery of alien life in three separate parts of their study. In the first case, they examined media reports of past announcements about the discovery of alien life, for example the announcement in 1996 that evidence of microbial life had been found in a Martian metorite.
Secondly, they asked a sample of over 500 people what their own reactions, and the reactions of the rest of humanity, would be to the hypothetical announcement of alien life.
Thirdly, the 500 people were split into two groups. Half were asked to read and respond to a real newspaper story announcing the discovery of fossilized Martian microbial life. The other half were asked to read and respond to a newspaper article announcing the creation of synthetic life by Craig Venter.
In all three cases the life was microbial in nature. Microbial life is the simplest life form, so it should be what we expect to find. This is certainly true in our own Solar System, since the existence of any other intelligent life has been ruled out here, while microbial life has not.
Also, in all three cases, the language of the respondents and the language in the media reports was analyzed for positive and negative words. A specialized piece of software called Linguistic Inquiry and Word Count (LIWC) was used. It’s text-analysis software that scans written language and identifies instances of words that reflect positive affect, negative affect, reward, or risk. (You can try LIWC here for fun, if you like.)
Analyzing Media Reports
The media reports used in the study were all from what the team considers reputable journalism outlets like The New York Times and Science Magazine. The reports were about things like unidentified signals from space that could have been alien in nature, fossilized microbial remains in meteorites, and the discovery of exoplanets in the habitable zones of other solar systems. There were 15 articles in total.
Overall, the study showed that language in media reports about alien life was more positive than negative, and emphasized reward rather than risk. So people generally find the potential of alien life to be a positive thing and something to be looked forward to. However, this part of the study showed something else: People were more positively disposed towards news of alien life that was microbial than they were towards alien life that could be present on exoplanets, where, presumably, it might be more than merely microbial. So, microbes we can handle, but something more advanced and a little doubt starts to creep in.
Reactions to Hypothetical Announcements of Alien Life
This part of the study aimed to assess people’s beliefs regarding how both they as individuals—and humanity as a whole—might react to the discovery of alien microbial life. The same LIWC software was used to analyze the written responses of the 500 people in the sample group.
The results were similar to the first part of the study, at least for the individuals themselves. Positive affect was more predominant than negative aspect, and words reflecting reward were more predominant than words reflecting risk. This probably isn’t surprising, but the study did show something more interesting.
When participants were asked about how the rest of humanity would respond to the announcement of alien life, the response was different. While positive language still outweighed negative language, and reward still outweighed risk, the differences weren’t as pronounced as they were for individuals. So people seem to think that others won’t be looking forward to the discovery of alien life as much as they themselves do.
Actual Reactions to the Discovery of Extraterrestrial Life
This is hard to measure since we haven’t actually discovered any yet. But there have been times when we thought we might have.
In this part of the study, the group of 500 respondents was split into two groups of 250. The first was asked to read an actual 1996 New York Times article announcing the discovery of fossilized microbes in the Martian meteorite. The second group was asked to read a New York Times article from 2010 announcing the creation of life by Craig Venter. The goal was to find out if the positive bias towards the discovery of microbial life was specific to microbial life, or to scientific advancements overall.
This part of the study found the same emphasis on positive affect over negative affect, and reward over risk. This held true in both cases: the Martian microbial life article, and the artificially created life article. The type of article played a minor role in people’s responses. Results were slightly more positive towards the Martian life story than the artificial life story.
Overall, this study shows that people seem positively disposed towards the discovery of alien life. This is reflected in media coverage, people’s personal responses, and people’s expectations of how others would react.
This is really just the tip of the iceberg, though. As the authors say in their study, this is the first empirical attempt to understand any of this. And the study was only 500 people, all Americans.
How different the results might be in other countries and cultures is still an open question. Would populations whose attitudes are more strongly shaped by religion respond differently? Would the populations of countries that have been invaded and dominated by other countries be more nervous about alien life or habitable exoplanets? There’s only conjecture at this point.
Maybe we’re novelty-seekers and we thrive on new discoveries. Or maybe we’re truth-seekers, and that’s reflected in the study. Maybe some of the positivity reflects our fear of being alone. If Earth is the only life-supporting world, that’s a very lonely proposition. Not only that, but it’s an awesome responsibility: we better not screw it up!
Still, the results are encouraging for humanity. We seem, at least according to this first study, open to the discovery of alien life.
But that might change when the first alien ship casts its shadow over Los Angeles.
It’s been 20 years since the first of the four Unit Telescopes that comprise the ESO’s Very Large Telescope (VLT) saw first light. Since the year 2000 all four of them have been in operation. One of the original goals of the VLT was to have all four of the ‘scopes work in combination, and that has now been achieved.
The instrument that combines the light from all four of the VLT ‘scopes is called ESPRESSO, which stands for Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations. ESPRESSO captures the light from each of the 8.2 meter mirrors in the four Unit Telescopes of the VLT. That combination makes ESPRESSO, in effect, the largest optical telescope in the world.
Combining the power of the four Unit Telescopes of the VLT is a huge milestone for the ESO. As ESPRESSO instrument scientist at ESO, Gaspare Lo Curto, says, “ESO has realised a dream that dates back to the time when the VLT was conceived in the 1980s: bringing the light from all four Unit Telescopes on Cerro Paranal together at an incoherent focus to feed a single instrument!” The excitement is real, because along with its other science goals, ESPRESSO will be an extremely powerful planet-hunting telescope.
“ESO has realised a dream that dates back to the time when the VLT was conceived in the 1980s.” – Gaspare Lo Curto, ESPRESSO instrument scientist.
ESPRESSO uses a system of mirrors, lenses, and prisms to transmit the light from each of the four VLT ‘scopes to the spectrograph. This is accomplished with a network of tunnels that was incorporated into the VLT when it was built. ESPRESSO has the flexibility to combine the light from all four, or from any one of the telescopes. This observational flexibility was also an original design goal for ESPRESSO.
The four Unit Telescopes often operate together as the VLT Interferometer, but that’s much different than ESPRESSO. The VLT Interferometer allows astronomers to study extreme detail in bright objects, but it doesn’t combine the light from the four Unit Telescopes into one instrument. ESPRESSO collects the light from all four ‘scopes and splits it into its component colors. This allows detailed analysis of the composition of distant objects.
ESPRESSO is a very complex instrument, which explains why it’s taken until now to be implemented. It works with a principle called “incoherent focus.” In this sense, “incoherent” means that the light from all four telescopes is added together, but the phase information isn’t included as it is with the VLT Interferometer. What this boils down to is that while both the VLT Interferometer and ESPRESSO both use the light of all four VLT telescopes, ESPRESSO only has the spatial resolution of a single 8.2 mirror. ESPRESSO, as its name implies, is all about detailed spectrographic analysis. And in that, it will excel.
“ESPRESSO working with all four Unit Telescopes gives us an enticing foretaste of what the next generation of telescopes, such as ESO’s Extremely Large Telescope, will offer in a few years.” – ESO’s Director General, Xavier Barcons
ESPRESSO is the successor to HARPS, the High Accuracy Radial velocity Planet Searcher, which up until now has been our best exoplanet hunter. HARPS is a 3.6 meter telescope operated by the ESO, and also based on an echelle spectrograph. But the power of ESPRESSO will dwarf that of HARPS.
There are three main science goals for ESPRESSO:
Measuring the Variation of the Fundamental Physical Constants
Analyzing the Chemical Composition of Stars in Nearby Galaxies
ESPRESSO will take highly precise measurements of the radial velocities of solar type stars in other solar systems. As an exoplanet orbits its star, it takes part in a dance or tug-of-war with the star, the same way planets in our Solar System do with our Sun. ESPRESSO will be able to measure very small “dances”, which means it will be able to detect very small planets. Right now, our planet-hunting instruments aren’t as sensitive as ESPRESSO, which means our exoplanet search results are biased to larger planets. ESPRESSO should detect more smaller, Earth-size planets.
Measuring the Variation of the Fundamental Physical Constants
This is where the light-combining power of ESPRESSO will be most useful. ESPRESSO will be used to observe extremely distant and faint quasars, to try and measure the variation of the fundamental physical constants in our Universe. (If there are any variations, that is.) It’s not only the instrument’s light-combining capability that allows this, but also the instrument’s extreme stability.
Specifically, the ESPRESSO will try to take our most accurate measurements yet of the fine structure constant, and the proton to electron mass ratio. Astronomers want to know if these have changed over time. They will use ESPRESSO to examine the ancient light from these distant quasars to measure any change.
Analyzing the Chemical Composition of Stars in Nearby Galaxies
ESPRESSO will open up new possibilities in the measurement of stars in nearby galaxies. It’s high efficiency and high resolution will allow astronomers to study stars outside of the Milky Way in unprecedented detail. A better understanding of stars in other galaxies is always a priority item in astronomy.
We’ll let Project Scientist Paolo Molaro have the last word, for now. “This impressive milestone is the culmination of work by a large team of scientists and engineers over many years. It is wonderful to see ESPRESSO working with all four Unit Telescopes and I look forward to the exciting science results to come.”
Ever since scientists confirmed the existence of seven terrestrial planets orbiting TRAPPIST-1, this system has been a focal point of interest for astronomers. Given its proximity to Earth (just 39.5 light-years light-years away), and the fact that three of its planets orbit within the star’s “Goldilocks Zone“, this system has been an ideal location for learning more about the potential habitability of red dwarf stars systems.
This is especially important since the majority of stars in our galaxy are red dwarfs (aka. M-type dwarf stars). Unfortunately, not all of the research has been reassuring. For example, two recent studies performed by two separate teams from Harvard-Smithsonian Center for Astrophysics (CfA) indicate that the odds finding life in this system are less likely than generally thought.
The first study, titled “Physical Constraints on the Likelihood of Life on Exoplanets“, sought to address how radiation and stellar wind would affect any planets located within TRAPPIST-1s habitable zone. Towards this end, the study’s authors – Professors Manasvi Lingam and Avi Loeb – constructed a model that considered how certain factors would affect conditions on the surface of these planets.
This model took into account how the planets distance from their star would affect surface temperatures and atmospheric loss, and how this might affect the changes life would have to emerge over time. As Dr. Loeb told Universe Today via email:
“We considered the erosion of the atmosphere of the planets due to the stellar wind and the role of temperature on ecological and evolutionary processes. The habitable zone around the faint dwarf star TRAPPIST-1 is several tens of times closer in than for the Sun, hence the pressure of the stellar wind is several orders of magnitude higher than on Earth. Since life as we know it requires liquid water and liquid water requires an atmosphere, it is less likely that life exists around TRAPPIST-1 than in the solar system.”
Essentially, Dr. Lingam and Dr, Loeb found that planets in the TRAPPIST-1 system would be barraged by UV radiation with an intensity far greater than that experienced by Earth. This is a well-known hazard when it comes to red dwarf stars, which are variable and unstable when compared to our own Sun. They concluded that compared to Earth, the chances of complex life existing on planets within TRAPPIST-1’s habitable zone were less than 1%.
“We showed that Earth-sized exoplanets in the habitable zone around M-dwarfs display much lower prospects of being habitable relative to Earth, owing to the higher incident ultraviolet fluxes and closer distances to the host star,” said Loeb. “This applies to the recently discovered exoplanets in the vicinity of the Sun, Proxima b (the nearest star four light years away) and TRAPPIST-1 (ten times farther), which we find to be several orders of magnitude smaller than that of Earth.”
Essentially, the team found that TRAPPIST-1, like our Sun, sends streams of charged particles outwards into space – i.e. stellar wind. Within the Solar System, this wind exerts force on the planets and can have the effect of stripping away their atmospheres. Whereas Earth’s atmosphere is protected by its magnetic field, planets like Mars are not – hence why it lost the majority of its atmosphere to space over the course of hundreds of million of years.
As the research team found, when it comes to TRAPPIST-1, this stream exerts a force on its planets that is between 1,000 to 100,000 times greater than what Earth experiences from solar wind. Furthermore, they argue that TRAPPIST-1’s magnetic field is likely connected to the magnetic fields of the planets that orbit around it, which would allow particles from the star to directly flow onto the planet’s atmosphere.
In other words, if TRAPPIST-1’s planets do have magnetic fields, they will not afford them any protection. So if the flow of charged particles is strong enough, it could strip these planets’ atmospheres away, thus rendering them uninhabitable. As Garraffo put it:
“The Earth’s magnetic field acts like a shield against the potentially damaging effects of the solar wind. If Earth were much closer to the Sun and subjected to the onslaught of particles like the TRAPPIST-1 star delivers, our planetary shield would fail pretty quickly.”
As you can imagine, this is not exactly good news for those who were hoping that the TRAPPIST-1 system would hold the first evidence of life beyond our Solar System. Between the fact that its planets orbit a star that emits varying degrees of intense radiation, and the proximity its seven planets have to the star itself, the odds of life emerging on any planet within it’s “habitable zone” are not significant.
The findings of the second study are particularly significant in light of other recent studies. In the past, Prof. Loeb and a team from the University of Chicago have both addressed the possibility that the TRAPPIST-1 system’s seven planets – which are relatively close together – are well-suited to lithopanspermia. In short, they determined that given their close proximity to each other, bacteria could be transferred from one planet to the next via asteroids.
But if the proximity of these planets also means that they are unlikely to retain their atmospheres in the face of stellar wind, the likelihood of lithopanspermia may be a moot point. However, before anyone gets to thinking that this is bad news as far as the hunt for life goes, it is important to note that this study does not rule out the possibility of life emerging in all red dwarf star systems.
As Dr. Jeremy Drake – a senior astrophysicist from the CfA and one of Garraffo’s co-authors – indicated, the results of their study simply mean that we need to cast a wide net when searching for life in the Universe. “We’re definitely not saying people should give up searching for life around red dwarf stars,” he said. “But our work and the work of our colleagues shows we should also target as many stars as possible that are more like the Sun.”
And as Dr. Loeb himself has indicated in the past, red dwarf stars are still the most statistically-likely place to find habitable worlds:
“By surveying the habitability of the Universe throughout cosmic history from the birth of the first stars 30 million years after the Big Bang to the death of the last stars in 10 trillion years, one reaches the conclusion that unless habitability around low-mass stars is suppressed, life is most likely to exist near red dwarf stars like Proxima Centauri or TRAPPIST-1 trillions of years from now.”
If there is one takeaway from these studies, it is that the existence of life within a star system does not simply require planets orbiting within the circumstellar habitable zones. The nature of the stars themselves and the role played by solar wind and magnetic fields also have to be taken into account, since they can mean the difference between a life-bearing planet and a sterile ball of rock!
If we want to send spacecraft to exoplanets to search for life, we better get good at building submarines.
A new study by Dr. Fergus Simpson, of the Institute of Cosmos Sciences at the University of Barcelona, shows that our assumptions about exo-planets may be wrong. We kind of assume that exoplanets will have land masses, even though we don’t know that. Dr. Simpson’s study suggests that we can expect lots of oceans on the habitable worlds that we might discover. In fact, ocean coverage of 90% may be the norm.
Normally, we give something a probability of occurring—in this case a habitable world with land masses—based on our data. And we’re more confident in our prediction if we have more data. So if we find 10 exoplanets, and 7 of them have significant land masses, we think there’s a 70% chance that future exoplanets will have significant land masses. If we find 100 exoplanets, and 70 of them have significant land masses, then we’re even more confident in our 70% prediction.
But the problem is, even though we’ve discovered lots of exoplanets, we don’t know if they have land masses or not. We kind of assume they will, even though the masses of those planets is lower than we expect. This is where the Bayesian methods used in this study come in. They replace evidence with logic, sort of.
In Bayesian logic, probability is assigned to something based on the state of our knowledge and on reasonable expectations. In this case, is it reasonable to expect that habitable exoplanets will have significant landmasses in the same way that Earth does? Based on our current knowledge, it isn’t a reasonable expectation.
According to Dr. Simpson, the anthropic principle comes into play here. We just assume that Earth is some kind of standard for habitable worlds. But, as the study shows, that may not be the case.
“Based on the Earth’s ocean coverage of 71%, we find substantial evidence supporting the hypothesis that anthropic selection effects are at work.” – Dr. Fergus Simpson.
In fact, Earth may be a very finely balanced planet, where the amount of water is just right for there to be significant land masses. The size of the oceanic basins is in tune with the amount of water that Earth retains over time, which produces the continents that rise above the seas. Is there any reason to assume that other worlds will be as finely balanced?
Dr. Simpson says no, there isn’t. “A scenario in which the Earth holds less water than most other habitable planets would be consistent with results from simulations, and could help explain why some planets have been found to be a bit less dense than we expected.” says Simpson.
Simpson’s statistical model shows that oceans dominate other habitable worlds, with most of them being 90% water by surface area. In fact, Earth is very close to being a water world. The video shows what would happen to Earth’s continents if the amount of water increased. There is only a very narrow window in which Earth can have both large land masses, and large oceans.
Dr. Simpson suggests that the fine balance between land and water on Earth’s surface could be one reason we evolved here. This is based partly on his model, which shows that land masses will have larger deserts the smaller the oceans are. And deserts are not the most hospitable place for life, and neither are they biodiverse. Also, biodiversity on land is about 25 times greater than biodiversity in oceans, at least on Earth.
Simpson says that the fine balance between land mass and ocean coverage on Earth could be an important reason why we are here, and not somewhere else.
“Our understanding of the development of life may be far from complete, but it is not so dire that we must adhere to the conventional approximation that all habitable planets have an equal chance of hosting intelligent life,” Simpson concludes.
It turns out that the TRAPPIST-1 star may be a terrible host for the TRAPPIST planets announced in February.
The TRAPPIST-1 star, a Red Dwarf, and its 7 planets caused a big stir in February when it was discovered that 3 of the rocky planets are in the habitable zone. But now more data is coming which suggests that the TRAPPIST-1 star is much too volatile for life to exist on its planets.
Red Dwarfs are much dimmer than our Sun, but they also last much longer. Their lifetimes are measured in trillions of years, not billions. Their long lives make them intriguing targets in the search for habitable worlds. But some types of Red Dwarf stars can be quite unstable when it comes to their magnetism and their flaring.
A new study analyzed the photometric data on TRAPPIST-1 that was obtained by the K2 mission. The study, which is from the Konkoly Observatory and was led by astronomer Krisztián Vida, suggests that TRAPPIST-1 flares too frequently and too powerfully to allow life to form on its planets.
The study identified 42 strong flaring events in 80 days of observation, of which 5 were multi-peaked. The average time between flares was only 28 hours. These flares are caused by stellar magnetism, which causes the star to suddenly release a lot of energy. This energy is mostly in the X-ray or UV range, though the strongest can be seen in white light.
While it’s true that our Sun can flare, things are much different in the TRAPPIST system. The planets in that system are closer to their star than Earth is to the Sun. The most powerful flare observed in this data correlates to the most powerful flare observed on our Sun: the so-called Carrington Event.The Carrington Event happened in 1859. It was an enormously powerful solar storm, in which a coronal mass ejection struck Earth’s magnetosphere, causing auroras as far south as the Caribbean. It caused chaos in telegraph systems around the world, and some telegraph operators received electric shocks.
Earth survived the Carrington Event, but things would be much different on the TRAPPIST worlds. Those planets are much closer to their Sun, and the authors of this study conclude that storms like the Carrington Event are not isolated incidents on TRAPPIST-1. They occur so frequently that they would destroy any stability in the atmosphere, making it extremely difficult for life to develop. In fact, the study suggests that the TRAPPIST-1 storms could be hundreds or thousands of times more powerful than the storms that hit Earth.
A study from 2016 shows that these flares would cause great disturbances in the chemical composition of the atmosphere of the planets subjected to them. The models in that study suggest that it could take 30,000 years for an atmosphere to recover from one of these powerful flares. But with flares happening every 28 hours on TRAPPIST-1, the habitable planets may be doomed.
The Earth’s magnetic field helps protects us from the Sun’s outbursts, but it’s doubtful that the TRAPPIST planets have the same protection. This study suggests that planets like those in the TRAPPIST system would need magnetospheres of tens to hundreds of Gauss, whereas Earth’s magnetosphere is only about 0.5 Gauss. How could the TRAPPIST planets produce a magnetosphere powerful enough to protect their atmosphere?
It’s not looking good for the TRAPPIST planets. The solar storms that hit these worlds are likely just too powerful. Even without these storms, there are other things that may make these planets uninhabitable. They’re still an intriguing target for further study. The James Webb Space Telescope should be able to characterize the atmosphere, if any, around these planets.
Just don’t be disappointed if the James Webb confirms what this study tells us: the TRAPPIST system is a dead, lifeless, grouping of planets around a star that can’t stop flaring.
NASA’s announcement last week of 7 new exoplanets is still causing great excitement. Any time you discover 7 “Earth-like” planets around a distant star, with 3 of them “potentially” in the habitable zone, it’s a big deal. But now that we’re over some of our initial excitement, let’s look at some of the questions that need to be answered before we can all get excited again.
What About That Star?
The star that the planets orbit, called Trappist-1, is a Red Dwarf star, much dimmer and cooler than our Sun. The three potentially habitable planets—TRAPPIST-1e, f, and g— get about the same amount of energy as Earth and Mars do from the Sun, because they’re so close to it. Red Dwarfs are very long-lasting stars, and their lifetimes are measured in the trillions of years, rather than billions of years, like our Sun is.
But Red Dwarfs themselves can have some unusual properties that are problematic when it comes to supporting life on nearby planets.
Red Dwarfs can be covered in starspots, or what we call sunspots when they appear on our Sun. On our Sun, they don’t have much affect on the amount of energy received by the Earth. But on a Red Dwarf, they can reduce the energy output by up to 40%. And this can go on for months at a time.
Other Red Dwarfs can emit powerful flares of energy, causing the star to double in brightness in mere minutes. Some Red Dwarfs constantly emit these flares, along with powerful magnetic fields.
Part of the excitement surrounding the Trappist planets is that they show multiple rocky planets in orbit around a Red Dwarf. And Red Dwarfs are the most common type of star in the Milky Way. So, the potential for life-supporting, rocky planets just grew in a huge way.
But we don’t know yet how the starspots and flaring of Red Dwarfs will affect the potential habitability of planets orbiting them. It could very well render them uninhabitable.
Will Tidal Locking Affect the Planets’ Habitability?
The planets orbiting Trappist-1 are very likely tidally locked to their star. This means that they don’t rotate, like Earth and the rest of the planets in our Solar System. This has huge implications for the potential habitability of these planets. With one side of the planet getting all the energy from the star, and the other side in perpetual darkness, these planets would be nothing like Earth.
One side would be constantly roasted by the star, while the other would be frigid. It’s possible that some of these planets could have atmospheres. Depending on the type of atmosphere, the extreme temperature effects of tidal locking could be mitigated. But we just don’t know if or what type of atmosphere any of the planets have. Yet.
So, Do They Have Atmospheres?
We just don’t know yet. But we do have some constraints on what any atmospheres might be.
Preliminary data from the Hubble Space Telescope suggests that TRAPPIST 1b and 1c don’t have extended gas envelopes. All that really tells us is that they aren’t gaseous planets. In any case, those two planets are outside of the habitable zone. What we really need to know is if TRAPPIST 1e, 1f, and 1g have atmospheres. We also need to know if they have greenhouse gases in their atmospheres. Greenhouse gases could help make tidally locked planets hospitable to life.
On a tidally locked planet, the termination line between the sunlit side and the dark side is considered the most likely place for life to develop. The presence of greenhouse gases could expand the habitable band of the termination line and make more of the dark side warmer.
We won’t know much about any greenhouse gases in the atmospheres of these planets until the James Webb Space Telescope (JWST) and the European Extremely Large Telescope (EELT) are operating. Those two ‘scopes will be able to analyze the atmospheres for greenhouse gases. They might also be able to detect biosignatures like ozone and methane in the atmospheres.
We’ll have to wait a while for that though. The JWST doesn’t launch until October 2018, and the EELT won’t see first light until 2024.
Do They Have Liquid Water?
We don’t know for sure if life requires liquid water. We only know that’s true on Earth. Until we find life somewhere else, we have to be guided by what we know of life on Earth. So we always start with liquid water.
A study published in 2016 looked at planets orbiting ultra-cool dwarfs like TRAPPIST-1. They determined that TRAPPIST 1b and 1c could have lost as much as 15 Earth oceans of water during the early hot phase of their solar system. TRAPPIST 1d might have lost as much as 1 Earth ocean of water. If they had any water initially, that is. But the study also shows that they may have retained some of that water. It’s not clear if the three habitable planets in the TRAPPIST system suffered the same loss of initial water. But if they did, they could have retained a similar amount of water.
There are still a lot of questions here. The word “habitable” only means that they are receiving enough energy from their star to keep water in liquid form. Since the planets are tidally locked, any water they did retain could be frozen on the planets’ dark side. To find out for sure, we’ll have to point other instruments at them.
Are Their Orbits Stable?
Planets require stable orbits over a biologically significant period of time in order for life to develop. Conditions that change too rapidly make it impossible for life to survive and adapt. A planet needs a stable amount of solar radiation, and a stable temperature, to support life. If the solar radiation, and the planet’s temperature, fluctuates too rapidly or too much due to orbital instability, then life would not be able to adapt to those changes.
Right now, there’s no indication that the orbits of the TRAPPIST 1 planets are unstable. But we are still in the preliminary stage of investigation. We need a longer sampling of their orbits to know for sure.
Pelted by Interlopers?
Our Solar System is a relatively placid place when it comes to meteors and asteroids. But it wasn’t always that way. Evidence from lunar rock samples show that it may have suffered through a period called the “Late Heavy Bombardment.” During this time, the inner Solar System was like a shooting gallery, with Earth, Venus, Mercury, Mars, and our Moon being struck continuously by asteroids.
The cause of this period of Bombardment, so the theory goes, was the migration of the giant planets through the solar system. Their gravity would have dislodged asteroids from the asteroid belt and the Kuiper Belt, and sent them into the path of the inner, terrestrial planets.
We know that Earth has been hit by meteorites multiple times, and that at least one of those times, a mass extinction was the result.
The TRAPPIST 1 system has no giant planets. But we don’t know if it has an asteroid belt, a Kuiper Belt, or any other organized, stable body of asteroids. It may be populated by asteroids and comets that are unstable. Perhaps the planets in the habitable zone are subjected to regular asteroid strikes which wipes out any life that gets started there. Admittedly, this is purely speculative, but so are a lot of other things about the TRAPPIST 1 system.
How Will We Find Out More?
We need more powerful telescopes to probe exoplanets like those in the TRAPPIST 1 system. It’s the only way to learn more about them. Sending some kind of probe to a solar system 40 light years away is something that might not happen for generations, if ever.
Luckily, more powerful telescopes are on the way. The James Webb Space Telescope should be in operation by April of 2019, and one of its objectives is to study exoplanets. It will tell us a lot more about the atmospheres of distant exoplanets, and whether or not they can support life.
Other telescopes, like the Giant Magellan Telescope (GMT) and the European Extremely Large Telescope (E-ELT), have the potential to capture images of large exoplanets, and possibly even Earth-sized exoplanets like the ones in the TRAPPIST system. These telescopes will see their first light within ten years.
What these questions show is that we can’t get ahead of ourselves. Yes, it’s exciting that the TRAPPIST planets have been discovered. It’s exciting that there are multiple terrestrial worlds there, and that 3 of them appear to be in the habitable zone.
It’s exciting that a Red Dwarf star—the most common type of star in our neighborhood—has been found with multiple rocky planets in the habitable zone. Maybe we’ll find a bunch more of them, and the prospect of finding life somewhere else will grow.
But it’s also possible that Earth, with all of its life supporting and sustaining characteristics, is an extremely unlikely occurrence. Special, rare, and unrepeatable.