Posted on by Nancy Atkinson

Exoplanets and the Search for Life in the Universe: Q&A with author Lee Billings

"Five Billion Years of Solitude" By Lee Billings

As far as our understanding of life in the Universe goes, right now, we’re it. But the past decade has brought discoveries of hundreds of planets orbiting other stars, some of which could potentially host life. Fellow science journalist Lee Billings has written a new book about the exciting field of searching for extrasolar planets. Five Billion Years of Solitude (read our review here) takes a look at some of the remarkable scientists and the incredible discoveries being made.

Earlier this week, we talked with Lee about the book and the future of how we might find a mirror of Earth.

Universe Today: What was the impetus behind writing this book – was there a specific event or moment where you said, ‘I want to write about astrobiology and the search for exoplanets,’ or was it a more gradual thing over time, where you were just intrigued by the whole expanding field?

Lee Billings
Lee Billings

Lee Billings: A little bit of both. I was definitely intrigued by the expanding field of searching for exoplanets, but it came all together for me after interviewing astronomer Greg Laughlin from the University of California, Santa Cruz in 2007 for an infographic about exoplanets. Near the end of our conversation, he mentioned — rather off the cuff — that if you tracked the smallest exoplanets found year by year and graphed them out over time, the trend-line would indicate that we would find an Earth-sized exoplanet by 2011. And I thought, “Holy crap, that’s just four years away!”

I was struck by the disconnect where we could see this plain-as-day data, but the wider world didn’t realize or appreciate this. It also bothered me that we’d soon be finding potentially habitable other worlds, and yet have great difficulty actually determining if they were habitable or even inhabited. And so there was this observational disconnect too, and a lot of people who didn’t seem to care there was this disconnect.

UT: And now that finding exoplanets has made front page news, are you encouraged by how people from afar are viewing this field?

LB: Yes and no. Exoplanets have been in the news for years now. 10 to 15 years ago when astronomers like Geoff Marcy and Michel Mayor were finding the first exoplanets — honkin’ huge balls of gas orbiting close to their stars — it would make front page news. Right now, there’s kind of been ‘exoplanet fatigue,’ where every couple of days a new exoplanet is being announced and exoplanets are even less in the news now because of this overload. And it’s going to keep happening, and I feel like by 2020 finding an Earth-sized planet in the habitable zone isn’t going to make front-page news because it’s going to be happening all the time and people are getting used to it.

UT: Kind of like the Apollo program all over again, where people soon got tired of watching people walk on the Moon?

LB: Yes! Even though I feel like more people in the public are aware of exoplanets being discovered and they even think exoplanets are cool, many think that finding thousands of exoplanets is just like stamp collecting — oh, we found another planet, let’s put it in the book and isn’t that one really pretty — that’s not what this is about. It’s about finding signs of life, finding a sense of context for ourselves in the wider universe, figuring out where Earth and all life upon it fits in this greater picture. I don’t think people are attuned to that side, but are being seduced by the stamp-collecting, horse-race nature of how finding exoplanets are depicted in the media. The emphasis isn’t on what it is going to take to really go out and find out more details about these exoplanets.

Frank Drake and the Drake Equation,
Frank Drake and the Drake Equation,

UT: You had the opportunity to talk with some of the great minds of our time — of course, Frank Drake is just such an icon of SETI and the potential for finding life out there in the Universe. But I think one of the most amazing things in your book that I’d never heard of before comes in one of the first chapters where you’re talking with Frank Drake and his idea for a spacecraft that uses the Sun as a gravitational lens to be able to see distant planets incredible detail. That’s amazing!

LB: If you use the Sun as a gravitational lens as sort of an ultimate telescope is really fascinating. As Drake said in the book, you can get some mind-boggling, insane data if you used the Sun as a gravitational lens, and align that with another gravitational lens in the Alpha Centauri system and you can send a high bandwidth radio signal in between those two stars with just the power of a cell phone. In visible light, you could possibly see things on a nearby exoplanet like night-time lighting, the boundary between land and sea, clouds, and weather patterns. It just boggles the mind.

There are other techniques out there that could in theory deliver these sorts of similar observations, but there’s just kind of a technical sweetness to the notion that the stars themselves could be the ultimate telescopes that we use to explore the universe and understand our place in it. I think that’s kind of a wild, poetic and elegant idea.

UT: Wow, that is so compelling. And speaking of compelling, can you talk about Sara Seager and the time you were able to spend with her, getting to know her and her work? Her story is quite compelling not to mention heartbreaking.

LB: She’s a remarkable woman and a brilliant scientist and I feel deeply privileged and honored to be able to tell her story — and that she shared so many details of her personal story with me. Really, she’s kind of a microcosm of the field at large. She crossed over from what she originally studied — from cosmology to exoplanetolgy — and her career seems to be defined by the refusal to accept that certain things might be impossible. She is always pushing the envelope and just keeps her eyes on the prize, so to speak, of finding smaller more Earth-like planets that could be habitable and finding ways of determining what they are actually like. There’s a parallel there between her path and astronomy at large, where there is tension between parts of the professional community. A lot of astronomy is concerned with studying how the universe began and the ancient, the distant, the dead. Exoplanetology is more concerned with the nearest stars to Earth and the planets — the new, the nearby and the living. I feel like she represents that shift and embodies some of that tension.

There’s also an element of tragedy, where she suffered a significant loss with the death of her husband, and had to find a way to get through it and get stronger coming out on the other side. I see similarities between that and what has happened in the field at large where we’ve seen big federally funded plans for future, next-generation telescopes like the Terrestrial Planet Finder, be scuttled on the rocky reefs of politics — and other things. It’s complicated why that’s happened, but there’s no denying that is HAS happened. 15 years ago we were talking about launching TPS by 2014 and now here we are, almost to 2014 and the James Webb telescope isn’t even launched and its eating up all the money for everything else. And now the notion of doing these big kinds of life-finding missions have fallen by the wayside. There’s been kind of the death of a dream, and the bright future that was forecast for what was going to happen for exoplanets doesn’t seem like it’s going to be. The community has had to respond to that and rebuild from that, and there doesn’t seem to be a lot of unity on what the best path forward is.

And also, Sara Seager is walking the line between the old way of big, federally funded projects and a new private, philanthropic path that may or may not be sustainable or successful, but it’s different and trying to do science in a new way. So maybe we don’t need to rely on big government or NASA to do this. Maybe we could ask philanthropists or crowd-funding or new enterprises that could help finance the projects in going forward. She’s got her feet in both worlds and is emblematic of the field right now.

Artistic representations of the only known planets around other stars (exoplanets) with any possibility to support life as we know it. Credit: Planetary Habitability Laboratory, University of Puerto Rico, Arecibo.
Artistic representations of the only known planets around other stars (exoplanets) with any possibility to support life as we know it. Credit: Planetary Habitability Laboratory, University of Puerto Rico, Arecibo.

UT: Yes, as you mention in the book, there is this tragic possibility that we may never find the things that these scientists are searching for — “mirror Earths, alien life, extraterrestrial intelligence, or a future beyond our lonely, isolated planet.” What do you see as the future of the search for exoplanets, in this age of funding cuts?

LB: What seems to be happening is that astronomers and planet hunters are needing to change their baselines and move their goalposts. In the past when people talked about space telescopes and finding signs of life, they were thinking of directly imaging planets around Sun-like stars and finding indications of life through studying the atmosphere and even surface features. The new way that is coming about and will likely happen in the next few decades, is an emphasis on smaller, cooler, less sun-like stars — the Red Dwarf or M-Dwarf stars. And it won’t be about directly imaging planets, but looking at transiting planets because it is easier to look at planets around lower-mass stars and at super-Earths that are easier to find and study. But these are rather alien places and we don’t know much about them, so it’s an exciting frontier.

But while transits are jackpots — in that you get all sorts of information like period, mass, radius, density and measures of the planet’s upper atmosphere — transits are very rare. If you think about the nearest thousand stars and if we are just looking for transits, that sort of search will only yield a fraction of the planets and the planetary diversity that exist. If you’re looking for life and potentially habitable planets, we really need a bigger sample and more than just transits to fill out the census of planets orbiting the stars around us.

I think missions like TESS and James Webb are going to be important, but I don’t think it will be enough. It will only leave us on the cusp of answering these bigger questions. I hope I’m wrong and that the emphasis on M-dwarfs and super-Earths and transits will be far more productive and surprising than anyone could have imagined or that there will be technology developed that are orders of magnitude cheaper, more affordable and better than these big telescopes.

But to answer the big questions more robustly in a way that is more satisfying to the public and data-hungry scientists, we’re probably going to have to make big investments, and invest the blood sweat and tears into building one of these big space telescopes. People in the astronomy community have been kicking and screaming about this because they realize the money just isn’t there.

But as someone once told me, there an economic inevitability to this in terms of how much the public can be engaged by these questions and how much they might hunger and thirst for finding other planets and life beyond our solar system. I feel like there is a strong push that could be made. I feel that the public would offer more support for these types of investments rather than for other projects, such as a a big space-based gravitational wave observatory or a big telescope devoted to studying dark energy.

Of course, we are living in this era of constrained and falling budgets, it’s going to be a really hard sell for any of these investments in astronomy, but pursuing the ancient, distant and dead instead of the new, nearby and living is probably a losing proposition, I do I wish astronomers the best of luck, but I hope they make the smart choice to prioritize the most publicly engaging science.

Artist's impression of the transiting exoplanet HAT-P-7b. Credit: NASA/ESA
Artist’s impression of the transiting exoplanet HAT-P-7b. Credit: NASA/ESA

UT: You write about the competition and sometimes the disdain that competing astronomers have for each other. Is this competition good, or should there be more unity in the field?

LB: In the interest of the community at large, I’d have to say unity is better and that some people have to wait their turn or reduce their expectations. I’m biased; I’m an advocate of exoplanet missions and these investments. But this is publicly funded science and I think it’s important for the community to be unified because it’s all too easy for the bean-counters in Washington to hear the discordant cacophony coming from the various astronomer hatchlings in the nest, and that there is no consensus except they are hungry and they want more.

They need to be unified to withstand the anti-scientific trends in funding we are seeing in our federal government right now. On the other hand, competition is important. But when you are doing publicly funded science, the scientists need to do a good job of making their case of why they should be funded.

UT: What was the most memorable experience in writing this book?

LB: That’s a really hard question! One of my great privileges and joys of writing the book was having access to these scientists and their work. But one of the most memorable things was visiting California’s Lick Observatory on Mount Hamilton in 2012 for the Transit of Venus. It was the last transit of Venus in our lifetime and it was amazing to stand there and think that the last time the transit was visible from Mount Hamilton was a century before, and realize all the changes that had happened in astronomy since then. This transit happened slowly over hours and it was amazing to stand there and realize, this is the last time in your life you’re going to see it and to wonder what is going to happen in the intervening years until this event occurs again.

But Lick Observatory was an appropriate place to be since that’s where some of the first exoplanets were found. When the last Transit of Venus took place, we hadn’t walked on the Moon, there were no computers, and we’ve had all these great discoveries in astronomy. I was thinking about what the world will be like in another hundred years or so, and thinking how while that is a long time for us, in the scale of planetary time, it is nothing at all! The Sun won’t have significantly aged and Venus will likely look exactly the same in 2117 for the next transit, but I would guess the Earth will be very different then. It’s kind of indicative of this transitional era we’re in. It was a very poignant moment for me.

UT: It’s similar to how Frank Drake talked about how he and his colleagues thought that searching for radio emissions from other civilizations would be so important in the search for extraterrestrial intelligence, but realizing that Earth’s radio emissions from our technology is waning and only lasted a short period of time.

LB: Yeah, perhaps when people look back at my book in the future, they might say, ‘wow, this guy was so blinkered and stupid — he didn’t see this technologies X, Y and Z coming and didn’t see monumental discoveries A, B, and C coming.’ I kind of hope that’s actually the case, because it will mean the search for extraterrestrial life and intelligence will have surpassed my wildest dreams. However, I didn’t try to predict what was going to happen, but just wanted to capture this strange and seemingly unique moment in time in which we are poised on the threshold of these immense discoveries that could totally transform our conception of the Universe and our place in it.

UT: Talking to you today, we can obviously tell how passionate you are about this subject and you were the perfect person to write about it!

LB: Thanks, Nancy!

Posted on by Elizabeth Howell

Baby Free-Floating Planet Found Alone, Away From A Star

Artist's conception of PSO J318.5-22. Credit: MPIA/V. Ch. Quetz

The planetary world keeps getting stranger. Scientists have found free-floating planets — drifting alone, away from stars — before. But the “newborn” PSO J318.5-22 (only 12 million years old) shows properties similar to other young planets around young stars, even though there is no star nearby the planet.

“We have never before seen an object free-floating in space that that looks like this. It has all the characteristics of young planets found around other stars, but it is drifting out there all alone,” stated team leader Michael Liu, who is with the Institute for Astronomy at the University of Hawaii at Manoa. “I had often wondered if such solitary objects exist, and now we know they do.”

Image from the Pan-STARRS1 telescope of the free-floating planet PSO J318.5-22, in the constellation of Capricornus. Credit: N. Metcalfe & Pan-STARRS 1 Science Consortium
Image from the Pan-STARRS1 telescope of the free-floating planet PSO J318.5-22, in the constellation of Capricornus. Credit: N. Metcalfe & Pan-STARRS 1 Science Consortium

The planet is about 80 light-years from Earth, which is quite close, and is part of a star group named after Beta Pictoris that also came together about 12 million years ago. There is a planet in orbit around Beta Pictoris itself, but PSO J318.5-22 has a lower mass and likely had a different formation scenario, the researchers said.

Astronomers uncovered the planet, which is six times the mass of Jupiter, while looking for brown dwarfs or “failed stars.” PSO J318.5-22’s ultra-red color stood apart from the other objects in the survey, astronomers said.

The free-floating planet was identified in the Pan-STARRS 1 wide-field survey telescope in Maui. Follow-up observations were performed with several other Hawaii-based telescopes, including the NASA Infrared Telescope Facility, the Gemini North Telescope, and the Canada-France-Hawaii Telescope.

The discovery will soon be detailed in Astrophysical Letters, but for now you can read the prepublished verison on Arxiv.

Source: Institute for Astronomy at the University of Hawaii

Posted on by Shannon Hall

Detecting the Magnetic Fields of Exoplanets May Help Determine Habitability

An artist's conception of two magnetic fields interacting in a bow shock. Image credit: NASA

Astronomers may soon be able to observe the shockwaves between the magnetic fields of exoplanets and the flow of particles from the stars they orbit.

Magnetic fields are crucial to a planet’s (and as it turns out a moon’s) habitability. They act as protective bubbles, preventing harmful space radiation from stripping away the object’s atmosphere entirely and even reaching the surface.

An extended magnetic field – known as a planetary magnetosphere – is created by the shock between the stellar wind and the intrinsic magnetic field of the planet. It has the potential to be huge. Within our own Solar System, Jupiter’s magnetosphere extends to distances up to 50 times the size of the planet itself, nearly reaching Saturn’s orbit.

When the wind of high-energy particles from the star hits the planetary magnetosphere, it interacts in a bow shock that diverts the wind and compresses the magnetosphere.

Recently a team of astronomers, led by PhD student Joe Llama of the University of St. Andrews, Scotland, have worked out how we might observe planetary magnetospheres and stellar winds via their bow shocks.

Llama took a careful look at the planet HD 189733b, located 63 light years away toward the constellation Vulpecula. From the Earth, the planet is seen to transit its host star every 2.2 days, causing a dip in the overall light from the system.

As a bright star, HD 189733b has been studied extensively by astronomers.  Data collected in July 2008 by the Canada-France-Hawaii telescope mapped the star’s magnetic field. While the magnetic field varied, it was on average 30 times greater than that of our Sun – meaning that the stellar wind is much higher than the solar wind.

This allowed the team to carry out extensive simulations of the stellar wind around HD 189733b – characterizing the bow shock created as the planet’s magnetosphere passes through the stellar wind.  With this information they were able to simulate the light curves that would result from the planet and the bow shock orbiting the star.

The bow shock leads the planet – causing the light to drop a little earlier than expected.  The amount of light blocked by the bow shock, however, will change as the planet moves through a variable stellar wind. If the stellar wind is particularly strong, the resulting bow shock will be strong, and the transit depth will be greater. If the stellar wind is weak, the resulting bow shock will be weak, and the transit depth will be less.

The video below shows the light curve of a bow shock and exoplanet.

“We found that the shockwave between the stellar and planetary magnetic fields will change drastically as activity on the star varies,” Llama told Universe Today. “As the planet passes through very dense regions of the stellar wind, so the shock will become denser, the material in it will block more light and therefore cause a larger dip in the transit making it more detectable.”

While there were no transit observations for this study, this theoretical outlook demonstrates that it will be possible to detect the bow shock, and therefore the magnetic field, of a distant exoplanet. Dr. Llama comments: “This will help us to better identify potentially habitable worlds.”

The paper has been accepted for publication in Monthly Notices of  The Royal Astronomical Society and is available for download here.

 

Posted on by Elizabeth Howell

‘Diamond’ Super-Earth’s Makeup Called Into Question In New Study

Illustration of 55 Cancri e, a super-Earth that’s thought to have a thick layer of diamond Credit: Yale News/Haven Giguere

A precious planet? Don’t think so fast, a new study says. The so-called “diamond super-Earth“, 55 Cancri e, may actually have a different composition than initially expected.

The team examined previous observations of the system, which is 40 light years from Earth, and said that there is less carbon (or what diamonds are made of) than oxygen in the planet’s star.

“In theory, 55 Cancri e could still have a high carbon to oxygen ratio and be a diamond planet, but the host star does not have such a high ratio,” stated University of Arizona astronomy graduate student Johanna Teske, who led the study.

“So in terms of the two building blocks of information used for the initial ‘diamond-planet’ proposal – the measurements of the exoplanet and the measurements of the star – the measurements of the star no longer verify that.”

Absorption of Light
Image Credit: www.daviddarling.info

The difficulty is it’s not so easy to send a spacecraft to a planet that is so far away from us, so we can’t do any close-up observations of it. This means that astronomers rely on methods such as absorption spectra (looking at what chemical elements absorb light at different wavelengths) of a star to see what it is made of.

The astronomers said there had been only a single oxygen line found in the last study, and they feel that 55 Cancri is cooler than the sun and has more metals into it. This conclusion would imply that the amount of oxygen in the star “is more prone to error.”

There are, however, a lot of moving pieces to this study. How do you know if a planet and star have similar compositions? How to accurately model a planet that you can’t see very well with conventional telescopes? How to best measure chemical abundances from afar? Teske acknowledged in a statement that her work may not be the definitive answer on this planet, so it will be interesting to see what comes out next.

The study has been accepted into the Astrophysical Journal. In the meantime, you can read the preprint version on Arxiv.

Source: University of Arizona

Posted on by Elizabeth Howell

Mercury’s Resonant Rotation ‘Should Be Common’ In Alien Planets

A global view of Mercury, as seen by MESSENGER. Credit: NASA

Three to two. That’s the ratio of the time it takes Mercury to go around the sun (88 days) in relation to its rotation (58 days). This is likely due to the influence of the Sun’s immense gravity on the planet. A new study confirms that finding, while stating something even more interesting: other star systems could see the same type of resonance.

Hundreds of confirmed exoplanets have been found so far, many of them in very tight configurations, the authors said. “Mercury-like states should be common among the hundreds of discovered and confirmed exoplanets, including potentially habitable super-Earths orbiting M-dwarf [red dwarf] stars,” they added. “The results of this investigation provide additional insight into the possibilities of known exoplanets to support extraterrestrial life.”

Habitability, of course, depends on many metrics. What kind of star is in the system, and how stable is it? How far away are the planets from the star? What is the atmosphere of the planet like? And as this study points out, what about if one side of the planet is tidally locked to its star and spends most or all of its time with one side facing the starshine?

Additionally, the study came up with an explanation as to why Mercury remains in a 3:2 orbit in opposition to, say, the Moon, which always has one side facing the Earth. The study took into account factors such as internal friction and a tidal “bulge” that makes Mercury appear slightly misshapen (and which could slow it down even further.) Basically, it has to do with Mercury’s early history.

From Orbit, Looking toward Mercury's Horizon. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
From Orbit, Looking toward Mercury’s Horizon. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

“Among the implications of the released study are, to name a few, a fast tidal spin-down, a relatively cold (i.e., not fully molten) state of the planet at the early stages of its life, and a possibility that the internal segregation and formation of the massive liquid core happened after Mercury’s capture into the resonance,” the press release added.

The results were presented today (Oct. 7) at the American Astronomical Society department of planetary sciences meeting held in Denver. A press release did not make clear if the study has been submitted for peer review or published.

Source: AAS Division of Planetary Sciences

Posted on by Elizabeth Howell

First Cloudy Alien Planet Spotted From Earth

Cloud map of Kepler-7b (left) in comparison to Jupiter (right). Credit: NASA/JPL-Caltech/MIT

Call it cloudy with a low chance of meatballs. The alien world Kepler-7b — a very reflective world in big telescopes — has clouds in its upper atmosphere. And scientists have actually been able to map those out, despite the planet’s great distance from Earth (at least 1,000 light-years away.)

It’s the first time scientists have been able to map out clouds on a world outside of the solar system. If we can see clouds, then we can begin to think about what a planet’s climate will be, making this an important milestone in understanding the conditions on other worlds.

“Kepler-7b reflects much more light than most giant planets we’ve found, which we attribute to clouds in the upper atmosphere,” stated Thomas Barclay, Kepler scientist at NASA’s Ames Research Center. “Unlike those on Earth, the cloud patterns on this planet do not seem to change much over time — it has a remarkably stable climate.”

Illustration of the Kepler spacecraft (NASA/Kepler mission/Wendy Stenzel)
Illustration of the Kepler spacecraft (NASA/Kepler mission/Wendy Stenzel)

Here’s how scientists got it done:

  • Preliminary observations with the Kepler space telescope –which was designed to hunt planets until a second reaction wheel failed earlier this year — found “moon-like phases” on Kepler-7b. These showed a bright spot on the western  hemisphere.
  • NASA’s Spitzer Space Telescope measured Kepler-7b’s temperature using infrared light, calculating it at between 1,500 and 1,800 degrees Fahrenheit (815 and 982 degrees Celsius.)
  • Something was clearly going on, as the planet is extremely close to its star; only 0.06 Earth-sun distances away. The temperature was too cool. They figured out that the light was reflected off cloud tops on the planet’s west side.

Another cool fact — Kepler-7b, like Saturn, would float if it was put in a big enough tub of water!

You can read more details in the technical paper online here. The study, which was led by the Massachusetts Institute of Technology, has been accepted to the Astrophysical Journal, but not published yet.

Source: NASA

Posted on by Shannon Hall

Magnetic Fields are Crucial to Exomoon Habitability

Artist's conception of an Earth-like exomoon orbiting a gaseous planet. Image credit: Avatar, 20th Century Fox

Astronomers believe that hidden deep within the wealth of data collected by NASA’s Kepler mission are minuscule signatures confirming the presence of exomoons. With such a promising discovery on the horizon, researchers are beginning to address the factors that may deem these alien moons habitable.

A new study led by Dr. René Heller from McMaster University in Canada and Dr. Jorge Zuluaga from the University of Antioquia in Colombia takes a theoretical look at habitability – exploring the key components that may make exomoons livable.  While stellar and planetary heating play a large role, it’s quickly becoming clear that the magnetic environments of exomoons may be even more critical.

An exoplanet’s habitability is first and foremost based on the circumstellar habitable zone – the temperature band around a star in which water may exist in its liquid state. Exomoons, however, have an additional set of constraints that affect their habitability. In a set of recent papers, Dr. Heller and Dr. Rory Barnes (from the University of Washington) defined a “circumplanetary habitable edge,” which is roughly analogous to the circumstellar habitable zone.

Here the question of habitability is based on the relationship between the exomoon and its host planet. The additional energy source from the planet’s reflected starlight, the planet’s thermal emission, and tidal heating in the moon may create a runaway greenhouse effect, rendering the exomoon uninhabitable.

One look at Io – Jupiter’s closest Galilean satellite – shows the drastic effects a nearby planet may have on its moon.  The strong gravitational pull of Jupiter distorts Io into an ellipsoid, whose orbit around the giant planet is eccentric due to perturbations from the other Galilean moons. As the orbital distance between Jupiter and Io varies on an eccentric orbit, Io’s ellipsoidal shape oscillates, which generates enormous tidal friction. This effect has led to over 400 active volcanic regions.

Note that this is an edge, not a zone.  It defines only an innermost habitable orbit, inside which a moon would become uninhabitable. The exomoon must exist outside this edge in order to avoid intense planetary illumination or tidal heating.  Exomoons situated in distant orbits, well outside the circumplanetary habitable edge, have a chance at sustaining life.

But the question of habitability doesn’t end here. Harmful space radiation can cause the atmosphere of a terrestrial world to be stripped off. Planets and moons rely heavily on magnetic fields to act as protective bubbles, preventing harmful space radiation from depleting their atmospheres.

With this in mind, Heller and Zuluaga set out to understand the evolution of magnetic fields of extrasolar giants, which are thought to affect their moons. It’s unlikely that small, Mars-sized exomoons will produce their own magnetic fields. Instead, they may have to rely on an extended magnetic field from their host planets.

This planetary magnetosphere is created by the shock between the stellar wind and the intrinsic magnetic field of the planet. It has the potential to be huge, protecting moons in very distant orbits.  Within our own Solar System Jupiter’s magnetosphere ends at distances up to 50 times the size of the planet itself.

Heller and Zuluaga computed the evolution of the extent of a planetary magnetosphere.  “Essentially, as the pressure of the stellar wind decreases over time, the planetary magnetic shield expands,” Dr. Heller told Universe Today. “In other words, the planetary magnetosphere widens over time.”

Evolution of the host planets magnetosphere for a
Evolution of the host planets magnetosphere (represented by the blue line) for Neptune-, Saturn-, and Jupiter-like planets. All increase over time by a varying amount.

The team applied these two models to three scenarios: Mars-sized moons orbiting Neptune-, Saturn-, and Jupiter-like planets. These three systems were always located in the center of the circumstellar habitable zone of a 0.7 solar-mass star. Here are the take-home messages:

1.) Mars-like exomoons beyond 20 planetary radii around any of the three host planets act like free planets around a star. They are well outside the habitable edge, experiencing no significant tidal heating or illumination. While their extreme distance is promising, they will never be enveloped within their host planet’s magnetosphere and are therefore unlikely to harbor life.

2.) Mars-like exomoons between 5 and 20 planetary radii face a range of possibilities. “Intriguingly, formation theory and observations of moons in the Solar System tell us that this is the range in which we should expect most exomoons to reside,” explains Dr. Heller.

For an exomoon beyond the habitable edge of a Neptune-like planet it may take more than the age of the Earth, that is, 4.6 billion years to become embedded within its host planet’s magnetosphere. For a Saturn-like planet it may take even longer, but for a Jupiter-like planet it will take less than 4.3 billion years.

3.) Mars-like exomoons inside 5 planetary radii are enveloped within the planetary magnetosphere early on but not habitable as they orbit within the planet’s habitable edge.

In order for an exomoon to be habitable it must exist well outside the habitable edge, safe from stellar and planetary illumination as well as tidal heating. But at the same time it must also exist near enough to its host planet to be embedded within the planet’s magnetosphere. The question of habitability depends on a delicate balance.

Dr. Zuluaga stressed that “one of the key consequences of this initial work is that although magnetic fields have been recognized as important factors determining the habitability of terrestrial planets across the Universe, including the Earth, Mars, and Venus, in the case of moons, the magnetic environment could be even more critical at defining the capacity of those worlds to harbor life.”

The paper has been accepted for publication in the Astrophysical Journal Letters and is available for download here.

Posted on by Elizabeth Howell

How Spitzer’s Focus Changed To Strange New Worlds

Artist's concept of NASA's Spitzer Space Telescope surrounded by examples of exoplanets it has looked at. Credit: NASA/JPL-Caltech

After 10 years in space — looking at so many galaxies and stars and other astronomy features — the Spitzer Space Telescope is being deployed for new work: searching for alien worlds.

The telescope is designed to peer in infrared light (see these examples!), the wavelength in which heat is visible. When looking at infrared light from exoplanets, Spitzer can figure out more about their atmospheric conditions. Over time, it can even detect brightness differences as the planet orbits its sun, or measure the temperature by looking at how much the brightness declines when the planet goes behind its star. Neat stuff overall.

“When Spitzer launched back in 2003, the idea that we would use it to study exoplanets was so crazy that no one considered it,” stated Sean Carey of NASA’s Spitzer Science Center, which is at the California Institute of Technology. “But now the exoplanet science work has become a cornerstone of what we do with the telescope.”

Of course, the telescope wasn’t designed to do this. But to paraphrase the movie Apollo 13, NASA was interested in what the telescope could do while it’s in space — especially because the planet-seeking Kepler space telescope has been sidelined by a reaction wheel problem. Redesigning Spitzer, in a sense, took three steps.

Classifying Galaxies
An example of Spitzer’s past work: This image from NASA’s Spitzer Space Telescope shows infrared light from the Sunflower galaxy, otherwise known as Messier 63. Spitzer’s view highlights the galaxy’s dusty spiral arms. Image credit: NASA/JPL-Caltech

Fixing the wobble: Spitzer is steady, but not so steady that it could easily pick out the small bit of light that an exoplanet emits. Engineers determined that the telescope actually wobbled regularly and would wobble for an hour. Looking into the problem further, they discovered it’s because a heater turns on to keep the telescope battery’s temperature regulated.

“The heater caused a strut between the star trackers and telescope to flex a bit, making the position of the telescope wobble compared to the stars being tracked,” NASA stated. In October 2010, NASA decided to cut the heating back to 30 minutes because the battery only needs about 50 per cent of the heat previously thought. Half the wobble and more exoplanets was more the recipe they were looking for.

The Spitzer Space Telescope. Credit: NASA
The Spitzer Space Telescope. Credit: NASA

Repurposing a camera: Spitzer has a pointing control reference sensor “peak-up” camera on board, which originally gathered up infrared light to funnel to a spectrometer. It also calibrated the telescope’s star-tracker pointing devices. The same principle was applied to infrared camera observations, putting stars in the center of camera pixels and allowing a better view.

Remapping a camera pixel: The scientists charted the variations in a single pixel of the camera that showed them which were the most stable areas for observations. For context, about 90% of Spitzer’s exoplanet observations are about a 1/4 of a pixel wide.

That’s pretty neat stuff considering that Spitzer’s original mission was just 2.5 years, when it had coolant on board to allow three temperature-sensitive science instruments to function. Since then, engineers have set up a passive cooling system that lets one set of infrared cameras keep working.

Source: NASA

Posted on by Shannon Hall

Planet Evaporates Due to Stellar Flare

An artist's conception of a disintegrating planet - creating a trail of dust - around its rocky star.

Solar flares – huge eruptions of charged particles from the Sun – present little threat to Earth. On a few rare occasions these particles may disrupt our communications systems and cause radio blackouts. But they tend to be more aesthetically pleasing than harmful. It’s certainly a sight to be seen as these energetic particles collide with our atmosphere, resulting in a cascade of colorful lights – the aurora borealis.

Fortunately our planet provides the protection necessary from such harmful space radiation. But not all planets are quite so lucky. Take for instance Kepler’s latest object of interest: KIC 12557548b, a super Mercury-size planet candidate. Astronomers have recently found that due to this star’s activity – producing massive stellar flares – the planet itself is evaporating.

Only last year, four different sources published evidence that this rocky planet was disintegrating. Thanks to Kepler, it quickly became clear that the total amount of light from KIC 12557548 as a function of time – the light curve of the system – dropped every 15.7 hours as a planet orbited it. But the amount of light blocked due to the transiting planet varied from 0.2% to more than 1.2%.

The amount of light blocked is dependent on the size of the planet. A Jupiter-size planet will block more light than a Mercury-size planet.  The variations here suggest a range for the size of the planet: from a super Mercury-sized planet to a Jupiter-sized planet.

But this wasn’t the planet’s only enigma. It also has an asymmetric light curve. The total light from the star drops steadily as the planet begins its transit, plateaus as the planet fully covers the disk of the star, and then increases as the planet ends its transit.  But the rate at which the light drops is much faster than the rate at which it increases.  It takes longer for the light curve to return to its original brightness, hinting at a tail of debris that trails the planet, continuing to block light.

Blah
The light curves of KIC 12557548b. The left-hand plot represents deep transits, whereas the right-hand plot represents more shallow transits.  Both plots show a clear asymmetry. Source: Brogi et al. 2012

It appears that the planet is evaporating – emitting small particles of dust into orbit, which then trails behind it. The varying transit depth reflects the amount of dust currently evaporating.

Recently a team from the University of Tokyo analyzed the system in more detail, attempting to explain why this tiny planet is evaporating. “We found that the transit depth negatively correlates with the modulation of the stellar flux,” Dr. Kawahara, lead author on the study, told Universe Today. “The dust amount increases when the planet is located in front of the star spots.”

The transit depth does not vary randomly, but every 22.83 days. This coincides with the modulation of the stellar flux, or simply the stellar rotation period.  Star spots may be indirectly detected by a star’s noticeable decrease in stellar flux.  Because these star spots are large (much larger than sunspots) they last for long periods of time, and may be used to deduce the star’s rotation period.

Kawahara et al. found that the transit depth periodically varies with the stellar rotation rate – finding a correlation between stellar activity and the rate at which the planet is evaporating.

“Energy from the star spots increases the amount of dust and atmosphere from the planet,” explains Dr. Kawahara. The extreme heat and wind is enough to speed up the motions of the dust molecules; making them fast enough to escape the planet’s gravitational pull.

Future spectroscopic studies may search for molecules in the evaporating atmosphere of KIC 12557548b.  But Dr. Kawahara remarks that due to the planet’s faintness it is unlikely. His best hope is that future studies may instead find a similar object closer to us, that may be more easy to study.

The finding is published in The Astrophysical Journal Letters and is available for download here.

Posted on by Elizabeth Howell

How Do You Find The Signs of Life On Alien Planets?

Artist's conception of the alien planet system orbiting Gliese 581. Credit: ESO/L. Calçada

One big challenge in astronomy is everything is so darn far away. This makes it hard to see the signs of life in planets, which are usually but tiny dots of light using the telescope technology we have today.

There are signs in Earth’s atmosphere that life is on the surface — methane from microbes, for example — and already scientists have years of research concerning ideas to find “biomarkers” on other planets. A new model focuses on a theoretical Earth-sized planet orbiting a red dwarf star, where it is believed biomarkers would be easier to find because these stars are smaller and fainter than that of the sun.

“We developed computer models of exoplanets which simulate the abundances of different biomarkers and the way they affect the light shining through a planet’s atmosphere,” stated Lee Grenfell, who is with the German Aerospace Center (DLR) institute of planetary science.

Preliminary work has already been done to find chemicals in the planet’s atmosphere (by looking at how they affect light that pass through the chemicals) particularly on large exoplanets that are close to their star (sometimes called “hot Jupiters“). Signs of life would be found through a similar process, but would be much fainter.

Artists Impression of a Red Dwarf (courtesy NASA)
Artist’s impression of a red dwarf (courtesy NASA)

The research team constructed a model of a planet similar to Earth, at different orbits and distances from a red dwarf stars. Their work shows a sort of “Goldilocks” effect (or, a condition that is “just right”) to find ozone when the ultraviolet radiation falls into the medium of a given range. If it is too high, the UV heats the middle atmosphere and obliterates the biomarker signal. Too low UV makes the signal very hard to find.

“We find that variations in the UV emissions of red-dwarf stars have a potentially large impact on atmospheric biosignatures in simulations of Earth-like exoplanets. Our work emphasizes the need for future missions to characterise the UV emissions of this type of star,” said Grenfell.

The research has plenty of limitations, he added. We don’t know what alien life would look like, we don’t know if planets near red dwarfs are a good place to search, and even if we found a signal that looked like life, it could have come from another process. Still, Grenfell’s team expects the model is a good basis on which to continue asking the question: is life really out there?

The research has been submitted to the journal Planetary and Space Science.

Source: European Planetary Science Conference