The saying goes that you should shoot for the moon because even if you miss, you’ll still land among the stars. This aphorism conceptualizes a dreamy metaphor, but a new discovery suggests that the idea of something attainable beyond our galaxy isn’t as far-fetched as it may seem.
In late February, NASA announced the astounding discovery of seven Earth-sized planets orbiting a single star in the constellation of Aquarius, named TRAPPIST-1. The star is comparable in size to Jupiter and is about 2,000 times less bright than our Sun. With only a small amount of emitted rays, TRAPPIST-1 is frigid, and creates a temperate climate among all seven planets.
These exoplanets may be ideal entities in the search for life beyond Earth due to their proximities and the few — but striking — conditions that make them similar to our planet.
At about 40 light years away, the exoplanets most notably resemble Earth in terms of size. Likewise, the temperatures of these seven planets are warm enough to sustain life and liquid water sources, as a result of the consistently temperate climate from TRAPPIST-1’s light emissions.
Differences, however, are also easy to identify. For instance, the TRAPPIST-1 solar system is far more compact than our solar system. This forces its planets to complete a full orbit in just 36 hours to 20 days, relative to the 365 days it takes for Earth to complete a full orbit around the sun.
Dan Tamayo, researcher at U of T’s Centre for Planetary Sciences and post-doctoral fellow at the Canadian Institute for Theoretical Astrophysics, suggests that even though the TRAPPIST-1 system is extraordinarily compact, there is a possibility that these exoplanets are tidally locked, like the moon is around Earth, which can result in unsustainable temperatures on certain faces of the planets.
“[TRAPPIST-1] is puny, barely hot enough to ignite nuclear fusion,” says Tamayo. “The planets are packed extremely close to the star. The innermost one is only about four times farther from the star than our moon is from us, and the outermost one orbits about 10 times closer than Mercury does around our sun.”
Tamayo continues, “It’s true that these planets could be tidally locked… always keeping the same face pointed toward the star. That would mean hot temperatures on the star-facing side, and frigid ones on the other side, unless you had a thick atmosphere to move warm air around. That certainly poses challenges for life, but everything’s possible.”
Still, the revelation of these seven planets has shocked astronomers and brings excitement to those who marvel at the cold depths of space. Not only is this the first time that such a large group of Earth-sized, potentially habitable planets have been found to orbit the same star system, but this is also a modern instance of humans expanding their conception of the planets that exist in the universe.
“This is a huge deal, way bigger than previous headlines for the most Earth-like planet found in the habitable zone to date,” says Tamayo. “We expect [that] there are billions of [exoplanets] in our galaxy, but planets this small are exceedingly hard to detect… Of the small planets we do discover, the vast majority are very close to their host star… which means they are typically at scalding hot temperatures where it is difficult to imagine life evolving.”
However, it is the potential for hosting water that sets the TRAPPIST-1 system apart from previously discovered solar systems, and designates them as exceptional entities for study.
TRAPPIST-1 exoplanets “are also very close to their host star, but their star is so tiny and lukewarm (as far as stars go!), that their surface temperatures are likely in the right range to host liquid water,” says Tamayo. “We’ve only really started detecting planets this small in the last few years. And that’s exciting, because it means they might have a solid surface capable of hosting life similar to us.”
As for the future study of these planets, astronomers from NASA and other space research centres, such as U of T’s Centre for Planetary Sciences, will continue to investigate the attributes of these exoplanets and the implications these attributes pose for life forms.
Tamayo adds, “Because the system is so close to Earth, this means we can get great information on their atmospheres. For example, it should be possible to detect whether or not these planets have ozone in their atmospheres. That wouldn’t be a slam dunk for life, but would easily make them the prime exoplanets to study.”
One of the important aspects of research will be the investigation of the gases present on these planets. “The idea is that oxygen and its products (like ozone) are extremely reactive,” says Tamayo. “If left alone in an atmosphere, they will react with rocks and other material and disappear as rust. The reason we have oxygen in our atmosphere is because it’s being constantly replenished by life.”
But the search for potential life doesn’t stop here. This record-breaking discovery is putting forth an array of new research topics.
“The big question is whether there are non-biological ways to make oxygen,” Tamayo explains. “The answer is yes, but you can bet finding ozone on TRAPPIST-1 planets would reinvigorate that line of research and spur creative ideas for ways of differentiating between biological and non-biological origins.”