Trappist-1 is an ultracool dwarf star nearly 40 light years from Earth. For astronomers, a star is an “ultracool dwarf” when it has low mass and a temperature under 2,700 kelvins (2,430 degrees Celsius). But Trappist-1 is “ultracool” even for nonscientists because it is home to seven Earth-size planets that scientists believe have conditions that could support liquid water and perhaps even life itself.
The discovery of those features means Trappist-1 now sets the record for having both the most Earth-size and potentially habitable planets around a single star. While scientists caution that the circumstances on those planets are very different from those that we know can sustain life, they are temperate and the right size to do just that. Excitement is building among the scientific community.
Located in the constellation Aquarius, Trappist-1 — the name comes from the Transiting Planets and Planetesimals Small Telescope, and the scientists who run the project are Belgian — is a little larger than Jupiter and whose mass is about 8 percent of our sun. In 2010, researchers identified it as a likely candidate for having planets since they observed that its brightness changes regularly, an indication that something is coming between it and Earth — something like a planet. In 2016, scientists concluded that the star had three planets in orbit round it. That announcement generated more attention and that scrutiny yielded four more planets.
The entire solar system — sun and planets — is very small. All seven of the planets are closer to Trappist-1 than Mercury is to our sun. The orbits of six of the planets range from 1.5 days to 12.3 days. (The orbit of the seventh is thought to be about 20 days, but it has only been observed once because it is so irregular.) That means they are very close to each other: An individual standing on the surface of one of the planets would be able to see geological features or even clouds on one of the other planets.
Five of the planets are the size of the Earth, while the remaining two are smaller, between the size of Earth and Mars. Normally, the planets’ proximity to their sun would mean they would be baked by its heat and reduced to a charred, crumbled mass. But this is an ultracool dwarf, which means it is considerably less hot than most stars, nor does it necessarily generate potentially life-killing levels of radiation. As a result, closeness to the sun is not fatal to the prospects for life.
All six inner planets are within what scientists refer to as the “temperate zone” where water might exist on the planet’s surface. When climate scientists examined the data, they concluded that the three closest planets are probably too near the sun, generating excessive greenhouse gases and associated warming. The remaining three planets, however, could have water. Scientists will then want to know what state — gas, solid or liquid — that water is in.
Water is important, but so too is geology. Planets likely need to be semisolid to sustain life. In our solar system, there are gassy planets, such as Neptune. The evidence thus far suggests that the six planets are rocky, like Earth. A rocky planet also means it is possible to generate gravitational stress which would then warm its interior. This is another factor that could influence the planet’s atmosphere, another foundational element of life. The observations thus far are not definitive, but it appears as though two of the closer planets are not gassy.
The proximity of Trappist-1 is one of the characteristics of this solar system that excites astronomers. Most solar systems that astronomers study are much further away and it takes considerably longer to get data and test various scenarios. Because it is so close to Earth, scientists can use the many telescopes scattered across our planet as well as those in space to check data and confirm hypotheses in a much shorter time period. One scientist has gone so far as to suggest that if there is indeed life in the Trappist-1 solar system, we may know within a decade.
This process will be expedited after the launch of the James Webb Space Telescope (JWST), which is scheduled to go into space in 2018. Researchers believe the JWST will allow them to study in detail the atmospheres of planets like those around Trappist-1 for the first time. It will be able to identify the key elements of those atmospheres, along with temperatures and surface pressures, all of which are critical in supporting life.
The JWST is the first in a new generation of space telescopes that will allow scientists to look further across the universe and deeper back in time. This new equipment will speed up and expand the search for exoplanets, while allowing us to better understand the cosmos. There is already an unprecedented excitement surrounding the discovery of the planets at Trappist-1, but astronomers believe this is only the beginning.
An ever-expanding universe with billions of stars provides billions if not trillions of opportunities for life to emerge. It is an exciting, sobering and scary thought.
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