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 is 10 times smaller than the sun and much dimmer and colder since it produces nearly a thousand times less radiation. 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 corners 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 conference of last Wednesday. It was worth it, since the new modifications allowed to record the presence of 5 more planets.
The 7 planets appear to orbit relatively close to the star, 20-200 times closer than the Earth orbit around the sun. Additionally, they are very close 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 it takes for that planet to go around the star. Knowing this, one can deduce the planet-star distance. Scientists were able to measure also the mass and the size of the planets. Mathematically, they could then derive the density, which can give clues about the material composition. 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 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 8% smaller than the Earth 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 that Webb will reveal about the molecular composition of the planets atmosphere. Not only will this help understand about the origin of the planets, it will also tell 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 chemical fingerprints 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 issues 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 and a possible answer may not be that far away. When such breakthrough discoveries are made new research scenarios open up and scientists join efforts to study them intensively. 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”. Indeed, studying the TRAPPIST-1 system will give insights into how this type of planets originated, and potentially about how planets formed, in general. The discovery of the TRAPPIST-1 system represents a great push to find answers explaining how celestial objects originated in the universe, and how life as we know it formed.
The idea that there may be other habitable planets in the universe should not make humans think that our own planet Earth can be exploited and drained with no concerns. The risk is that the myth of plausible alternative future worlds may become the excuse to continue destroying our own present world. In the name of economic growth, humans are exhausting natural resources by choosing fossil fuels that produce greenhouse gasses over renewable forms of energy, by performing large-scale deforestation, by favoring extensive farming and massive use of pesticides that will eventually ruin the ecosystem, by irresponsibly consuming and disposing of waste. These actions of sabotage will likely damage our planet Earth permanently. Shouldn’t we instead take a more responsible behavior to try to save the Earth from devastation? Even if we wanted to desperately reach these new habitable zones, nowadays it would take a minimum of 39 years, assuming we could travel at the speed of light, or actually 44 million years with a jet plane.
Scientists are looking out to find routes to new worlds. Meanwhile, shall we take our own spiritual journey to re-learn how to value what we already have and it is very precious?