In recent years, the number of new planets known to exist beyond our solar system has increased dramatically. But the most tantalizing discoveries of all are those so-called exoplanets that can potentially support life as we know it.
In February of 2017, NASA announced the first known planetary system containing seven Earth-sized planets orbiting around a single star. “This discovery could be a significant piece in the puzzle of finding habitable environments, places that are conducive to life,” said Thomas Zurbuchen, NASA Science Mission Directorate associate administrator in Washington. Three of these new planets are orbiting well within the habitable region around the parent star. This is the so-called Goldilocks zone, which is the region around a star where the temperatures are reasonable for life and liquid water can exist on a planetary surface given sufficient atmospheric pressure.
This seven-planet system is named TRAPPIST-1, after the Transiting Planets and Planetesimals Small Telescope, in Chile. The star itself is an ultracool dwarf star, about 10 times smaller and 2.5 times cooler than our sun. Astronomers used TRAPPIST to discover three new planets in this system and published their findings in 2016. NASA subsequently coordinated with other ground-based facilities and employed the Spitzer Space Telescope to confirm these findings. They discovered additional worlds in the process. Using the new data, the team precisely measured the sizes of the seven planets and developed preliminary mass and density estimates for most of them.
What Are the TRAPPIST-1 Planets Like?
The TRAPPIST-1 exoplanets are believed to be rocky worlds, similar in size and density to our solar system’s inner terrestrial planets. On a galactic scale, the TRAPPIST-1 system is located right next door. It’s only about 40 light-years from Earth in the constellation of Aquarius. This is a compact planetary system compared to ours. The whole thing is much smaller in diameter than the orbit of Mercury. A year on the innermost planet in only 1.5 Earth days, while the outermost planet’s year is only 18.8 days. Astronomers believe the planets are “tidally locked,” meaning that one side of the planet always faces the star, while the other side is in perpetual night.
While there is currently no way to determine what the surfaces and atmospheres of these worlds might actually look like, the exploration of our own solar system has shown that almost anything is possible. If you could travel to the TRAPPIST-1 system, the views would likely be spectacular. The planets are close together and would appear prominently in each other’s skies and frequently transit the star. In some cases, they would appear much larger than the moon as seen from Earth. On any of the planets with an atmosphere, the star would remain fixed in the sky on the daylight side, and its dim reddish light would bathe the world in a kind of perpetual sunset.
What Can We Expect in the Coming Years?
As we continue to explore TRAPPIST-1 over the next decade, observations will focus on determining whether these planetary atmospheres contain any water. If they do in abundance, there’s a good chance they also have liquid water on their surfaces. So far, liquid water has not (yet) been found on any new planet beyond the solar system and that would be a significant discovery and a critical factor in assessing potential habitability.
How Can NASA Find Out?
Astronomers will employ several methods to figure this out. Fortunately, the TRAPPIST-1 system is aligned with respect to Earth such that the planets can be seen to pass in front of the star, called transiting, and behind the star as they move in their orbits. Careful observations of these movements will be used in several ways.
First, NASA’s planet-hunting Kepler space telescope is already at work making measurements of the star’s minuscule changes in brightness when the planets transit. This is how the first three new planets were discovered. These observations will help refine the properties of the known planets and search for additional planets in the system. Astronomers will also measure the drop in brightness of the whole system when a planet passes behind the star. This negative measurement can be used to determine the relative brightness of each planet, which can help to ascertain what’s in each of the atmospheres.
Another critical observation will be analyzing the light that passes through the atmospheres of each new planet as they transit. The Hubble Space Telescope and ground-based observatories will be used to examine the light and try to identify what compounds are in the atmospheres of each world. Scientists will be especially keen on finding gases such as oxygen, which could be an indicator of biological life.
NASA’s James Webb Space Telescope (JWST)
These near-term observations will help astronomers plan for future studies using NASA’s upcoming James Webb Space Telescope. The Webb Telescope is the most advanced and powerful space telescope ever built. Its giant mirror will provide seven times greater light gathering power compared with the Hubble Space Telescope. The Webb Telescope’s primary mission is Infrared Astronomy. The spacecraft is carefully designed to provide an extremely cold environment for its infrared instruments, which are far more sensitive than anything previously available. When launched in 2018, the telescope will be positioned in a halo orbit about four times further from Earth than the moon, at a gravitationally stable location known as the second Lagrange point (L2).
Forty light years away from TRAPPIST-1, NASA will be able to detect water, methane, oxygen, ozone and other atmospheric components, and will analyze planetary and surface pressures and temperatures. These are critical factors in assessing potential habitability. Dr. Alberto Conti, astrophysicist and innovation manager at Northrop Grumman, believes that the use of tools like the Webb Telescope will inevitably lead to the discovery of watery planets. And possibly, life.