Directly Imaging Exoplanets or: Seeing Alien Worlds

Apr 13, 2016

By Mandeep S.S. Gill


Professor Bruce Macintosh (pictured above) of KIPAC is the primary protagonist of “In Search of Ancient Jupiters,” an excellent and compelling piece by Lee Billings in the Aug 2015 edition of the popular science magazine Scientific American (SciAm), and in the article he gives a very human perspective on the race to find and see this class of exoplanets directly vs. using the indirect means that most recent methods have focused on.


Above: The planet that Macintosh’s team found is indicated by the bright spot near the letter “b.”  The dashed line indicates the distance of Saturn’s orbit from our own Sun (Credit: Gemini/GPI team.)


Though the story focuses around Macintosh and recent advances in the research program of the Gemini Planet Imager (GPI), an advanced high-contrast imaging instrument on the Gemini South Telescope in Chile that he leads as Principal Investigator, his old friend Jean-Luc Beuzit is also featured as leading a competing instrument (called SPHERE), mounted on a different telescope high in the Chilean Andes. However, Beuzit is shown in the piece not to be an “archenemy,” but a friendly competitor in the best tradition of scientific rivalries, and both teams will ultimately complement one another's discoveries, for certain.

Above: Macintosh (in center) and his team quite excited about the successful deployment of the GPI instrument, and seeing its first-light images.

It is truly an exciting time for those who yearn to find out if we are really alone in the great dark inky vastness of the Universe, or whether there is some kind of other life out there, because we are now on the verge of being able to image the other planets out there in alien stellar systems. The biggest payoff of that kind of search would be seeing the aliens looking back right at us, of course.  And the GPI team is taking one giant step towards that day, because as the SciAm piece states, Macintosh is:

...[N]ot interested in finding planets like most astronomers do, watching for months or even years as subtle shifts in a star’s motion or brightness gradually reveal the presence of an unseen world. He is after instant gratification: he intends to take actual pictures of remote planets, to see them as points of light circling their distant stars, to look on their ... faces across the gulf of light-years.


Indeed, one of the most amazing things about the current generation of direct planet imaging instruments is that by taking even a fuzzy picture of a planet next to the glaring backdrop of the star it is orbiting around, astronomers are able to “learn a lot about that world’s composition, climate and possibilities for life.”


Above: The Gemini South Telescope in Chile, at sunrise (Image Courtesy: Kate Follette.)


While the ultimate goal is, of course, to image something like an Earth around another star, for now getting the images of much larger Jupiter-sized gas giants is what our instruments are capable of doing.  But far from regarding this as a current-day consolation prize, it’s important to recognize that in fact:

Among experts, it is an embarrassing open secret that no one really knows how the largest object orbiting our sun came to be. But the experts desperately want to find out because Jupiter and other giant planets are the architects of planetary systems, shaping all that surrounds them. 

 So that the more data points we gather from other stellar systems and learn about the varieties of those systems, the more we can learn about planetary formation in general, and just how our own system came to be.

In fact, to understand just how significant Jupiter has been to us here on the Earth, it will help to review astronomers’ current understanding and belief about our Jovian history, which is that:

Jupiter probably also migrated early in its life, but for reasons unclear, its migration was only temporary and did not bring the giant planet within spitting distance of the sun. Instead it perhaps ventured about as far in as present-day Mars, before retreating back to the outer solar system, where it has stayed ever since. And although the motions of a giant planet can sabotage a planetary system’s habitability, in Jupiter’s case they seem to have made our solar system a more hospitable place. At the least, Jupiter’s peregrinations are thought to have flung water-rich comets and asteroids down to our already formed planet, delivering life-giving oceans. At most, Jupiter’s plunge into the inner solar system might have even cleared out other preexisting planets, allowing Earth to form in the first place.

And from a slightly more frightening perspective:

Even so, what Jupiter gives, it could take away. Millions of years from now, Jupiter may pummel our planet again with more giant asteroids or comets, generating cataclysmic impacts that would boil off our oceans and steam-cook our biosphere.

That doesn’t sound very promising at all. It would be good to learn how this is working in other systems, just to make some plans, know when to sell all of our mutual funds, etc.

Now, there are two primary competing theories for how gas giants in stellar systems form, which go by the names of “disk instability” and “core accretion.”  Studying distant systems which are still in the process of cooling down could shed much light on which of these are more correct — and our own history, and future, as well.

Above: The team with GPI instrument, mounted at the bottom of the telescope (L to R: Kate Follette, Eric Nielsen,  Bruce Macintosh, Vanessa Bailey, and Ashley Chontos.) You can tell they have some serious affection for this contraption, indeed (Credit: Kate Follette.)

And indeed, GPI is well on its way to new discoveries:

On the final night of the six-day run, the GPI team finds its first planet, orbiting a 20-million-year-old star at twice the Jupiter-sun distance... Subsequent observations show it to be between two and three times Jupiter’s mass, with a methane-filled atmosphere hot enough to melt lead. The planet is 100 light-years from Earth, but it is the closest thing to Jupiter astronomers have ever seen.

Looking towards the future, the article further discusses the three “Extremely Large Telescopes” that are currently under planning stages, with massive mirrors that will gather 10 or more times the light of anything currently operational on Earth. At least one of these in fact is at the stage where the mountaintop it is slated to go on is being prepared for its eventual construction, and once it is operational and has an advanced version of GPI on it, it would able to image not only self-luminous Jupiters but also cooler, 1,000 times fainter, potentially habitable planets orbiting the sun’s nearest neighboring stars. A dedicated direct-imaging mission in space could then probe them even further, seeking signs of life. Provided, that is, such worlds are even there to see. The prospect of getting those images, glimpsing alien Earths, is what motivates many of the people behind projects such as GPI. 

Above: A flying denizen of our own planet (a condor) silhouetted against the dome of another telescope called SOAR,  about 2 miles from the Gemini site (Credit: Dmitry Savransky.)

Bringing it all back down to Planet Earth and what it means for us denizens of this small green and blue planet in our little corner of the Universe, Macintosh’s quote that ends the piece holds some lessons for all of us who live here, even as our species yearns in the long-term always towards the heavens:

I see everything we’re doing now as steps along the road toward a picture of another Earth. Someday we will have that picture. If we finally get results on the fraction of small, rocky planets that include really relevant things—which ones have oceans, atmospheric oxygen, and so on—and that number turns out to be very tiny, well, that’s probably pretty important. It may make no practical difference to the progression of our civilization for a very long time, but philosophically, being able to say that ‘ours is the only place like this within 1,000 light-years,’ maybe that would cause us to try a little harder not to screw it up.

Above: GPI teammember Ashley Chontos taking a break from searching for planets around other stars, and enjoying some of the beauty of the third planet circling around our own star (Credit: Kate Follette.)


(If you happen to have an online subscription to SciAm Magazine you can read the whole thing, otherwise you'll see only the first couple of paragraphs at the link and will need to go to your local library to read it for free in print!).…/inside-the-race-to-gl…/

All excerpts from 'In Search of Alien Jupiters,' by Lee Billings, Scientific American, August, 2015.

Reproduced with Permission Scientific American, a division of Nature America, Inc. All rights reserved.

---------------- Further Reading:

Discovery and spectroscopy of the young Jovian planet 51 Eri b with the Gemini Planet Imager