By Chiara Bertipaglia, Postdoctoral Research Scientist at Columbia University and KnowScience editor
On Wednesday 22nd February NASA announced the discovery of 7 rocky planets just 39 light years (235 trillion miles) away from the Earth. The study, published in the scientific journal Nature, is fruit of collaboration between astronomers at the University of Liege in Belgium and NASA’s laboratories at Caltech in California.
These 7 exoplanets (planets beyond our solar system) appear to be rocky and are part of the TRAPPIST-1 system, meaning they all orbit around the same star called TRAPPIST-1. The TRAPPIST-1 system was discovered just a year ago by the Transiting Planets and Planetesimal Small Telescope (TRAPPIST) in Chile, reporting, at the time, only 2 planets around the star. TRAPPIST-1 is an ultracool dwarf, a type of star emitting infrared light, impossible to see by naked eye. It was therefore an ideal candidate to be studied by the infrared space telescope Spitzer, which was launched in space in the Summer of 2003, to explore the angles of the universe that are inaccessible to normal optical telescopes. To properly record the light emitted by TRAPPIST-1, Spitzer had to be modified directly “in space” by astronauts, said Sean Carey, manager of NASA’s Spitzer Science Center at Caltech/IPAC during the press release of last Wednesday. It was worth it since the new modifications allowed to record the presence of 5 more planets. TRAPPIST- 1 is 10 times smaller than the sun and produces nearly a thousand times less radiation. The infrared emission spectrum of TRAPPIST-1 is what makes it dimmer and colder than our sun, and allows the planets to orbit relatively close to it (20-200 times closer than the Earth orbit around the sun).
The 7 planets appear to orbit very closely to each other: if you were standing on the surface on one of them, you would see the others not as small bright spots in the sky, but rather as big spheres, as we are used to seeing the moon. Their position relative to each other lead the scientists speculate that they may interact “gravitationally”, that is to say they may be tightly locked to each other due to the Gravitational force. This would cause them to face the star always with the same side (the other one being constantly in the dark), and not to spin like the Earth.
Which parameters is the telescope able to record precisely? Spitzer can measure the star brightness very accurately. However, it doesn’t actually image each single planet. Instead, it measures the amount of light that TRAPPIST-1 is dimmed by when each planet passes in front of it, partially eclipsing it. This parameter tells the size of the planet. Moreover, one can calculate the frequency with which each planet transits in front of the star, and this tells about how long the year is for that planet. Know how long it takes for the planet to go around the star, one can deduce its distance from the star. Scientists were able to measure also the mass and the size of the planets. Mathematically, they could then derive the density, which gave initial clues about the material composition of the planets. This is how they concluded that these are rocky planets, and not watery or gaseous.
Why is the scientific community so excited about this discovery? Because 3 of these planets fall in the so-called habitable zone, as their distance from TRAPPIST-1 may permit the presence of liquid water and therefore support life as we know it. The size of these 3 planets is quite comparable to the one of the Earth. TRAPPIST-1e is located in the innermost ring of the habitable zone, therefore it is the habitable planet closest to the star. It is very similar to the Earth in size and receives about the same amount of star light that we receive from the sun, supporting the speculation that on this planet there may be atmospheric conditions similar to ours. It was possible to actually measure geo-parameters that suggest water-rich composition of the soil of TRAPPIST-1e.
What is still to be studied? The Spitzer, Hubble, and Kepler telescopes are working top gear to help astronomers plan follow-up studies using NASA’s upcoming James Webb Space Telescope, launching in 2018. The hope is the Webb will reveal about the molecular composition of the planets’ atmosphere. Not only will this help figure out the origin of the planets, it will also tell us about the chemical processes happening on their surface as well as temperature and pressure, key factors in assessing their potential of supporting life as we know it. The Hubble space telescope is currently challenging this task through a technique known as “transmission spectroscopy”, which detects the fingerprints of different chemical species present in the air, said Nikole Lewis, astronomer at the Space Telescope Science Institute in Baltimore. With much greater sensitivity, the Webb telescope will be able to detect the presence of water, methane, oxygen, ozone, and other molecules that could indicate sing of life.
There are lots of ultracool dwarfs similar to TRAPPIST-1 in the universe and scientists are setting out to observe 1000 of them, to figure out whether potentially there may be more of these planet systems with habitable zones out there. The race to discover new forms of lives in the universe obviously raises questions and “philosophical” matters to consider: are we really alone in the universe? This is certainly one of the most long-standing questions that philosophers and intellectuals have discussed and written about. But is the scientific community really only focused on finding new forms of life to get in touch with them? When such breakthrough discoveries are made, scientists are mostly very excited about the possibility of genuinely, “simply” studying new realities and satisfy intellectual curiosity. In the NASA press release of last Wednesday, Sara Seager, professor of planetary science and physics at MIT, Cambridge said that astronomers now consider the TRAPPIST-1 system “a veritable laboratory for studying planets orbiting very cool, very small, very dim red stars that are so incredibly different from our sun (…) to test many people’s theories about these worlds”.
The idea that there may be other habitable planets out there should not make humans think that our own planet Earth can be consumed with no concerns whatsoever and tossed away like an old object. The risk is that the myth of plausible alternative future worlds may become the excuse to continue destroying our very own present world. Should we rather join efforts to try to save the Earth from being devastated by deforestation, emission of greenhouse gasses and irresponsible consumption and disposal of waste? In any case, even if we wanted to desperately reach these new habitable zones, nowadays it would take a minimum of 39 years if we were able to travel at the speed of light. With a modern jet plane, it would take 44 million years.
Astrophysicists are taking care of finding new routes to new worlds. Meanwhile, shall we take our own spiritual journey to re-learn how to value what we already have, and it’s very precious?
goo.gl/yQEXJ1 (nasa website)
goo.gl/fmhm2x (original nature paper)
goo.gl/whTwiP (lay audience article)