Scientists Have Discovered An Entire System Of Earth-Like Exoplanets
In the latest news about the continued search for Earth-like planets outside the Solar System, NASA announced today the discovery of an entire system of Earth-like exoplanets orbiting a star just 40 light-years away:
Not just one, but seven Earth-size planets that could potentially harbor life have been identified orbiting a tiny star not too far away, offering the first realistic opportunity to search for signs of alien life outside of the solar system.
The planets orbit a dwarf star named Trappist-1, about 40 light years, or some 235 trillion miles, from Earth. That is quite close in cosmic terms, and by happy accident, the orientation of the orbits of the seven planets allows them to be studied in great detail.
One or more of the exoplanets in this new system could be at the right temperature to be awash in oceans of water, astronomers said, based on the distance of the planets from the dwarf star.
“This is the first time so many planets of this kind are found around the same star,” said Michael Gillon, an astronomer at the University of Liege in Belgium and the leader of an international team that has been observing Trappist-1.
They could even discover convincing evidence of aliens.
“I think that we have made a crucial step toward finding if there is life out there,” said Amaury H.M.J. Triaud, an astronomer at the University of Cambridge in England and another member of the research team. “Here, if life managed to thrive and releases gases similar to that we have on Earth, then we will know.”
The findings appeared Wednesday in the journal Nature.
Telescopes on the ground now and the Hubble Space Telescope in orbit will be able to discern some of the molecules in the planetary atmospheres. The James Webb Space Telescope, scheduled to launch next year, will peer at the infrared wavelengths of light, ideal for studying the dimmer light coming from Trappist-1.
Comparisons among the different conditions of the seven will also be revealing.
“The Trappist-1 planets make the search for life in the galaxy imminent,” said Sara Seager, an astronomer at the Massachusetts Institute of Technology who was not a member of the research team. “For the first time ever, we don’t have to speculate. We just have to wait and then make very careful observations and see what is in the atmospheres of the Trappist planets.”
Even if the planets all turn out to be lifeless, scientists will have learned more about what keeps life from flourishing.
Astronomers always knew other stars must have planets, but until a couple of decades ago, they had not been able to spot them. Now they have confirmed more than 3,400, according to the Open Exoplanet Catalog. (An exoplanet is a planet around a star other than the sun.)
While the Trappist planets are about the size of Earth — give or take 25 percent in diameter — the star is very different from our sun.
Trappist-1, named after a robotic telescope in the Atacama Desert of Chile that the astronomers initially used to study the star, is what astronomers call an “ultracool dwarf,” with only one-twelfth the mass of the sun and a surface temperature of 4,150 degrees Fahrenheit, much cooler than the 10,000 degrees of heat radiating from the sun. Trappist is a shortening of Transiting Planets and Planetesimals Small Telescope.
Until the last few years, scientists looking for life elsewhere in the galaxy have focused on finding Earth-size planets around sun-like stars. But it is difficult to pick out the light of a planet from the glare of a bright star. Small dim dwarfs are much easier to study.
Last year, astronomers announced the discovery of an Earth-size planet around Proxima Centauri, the closest star at 4.24 light years away. That discovery was made using a different technique that does not allow for study of the atmosphere.
Trappist-1 periodically dimmed slightly, indicating that a planet might be passing in front of the star, blocking part of the light. From the shape of the dips, the astronomers calculate the size of the planet.
Trappist-1’s light dipped so many times that the astronomers concluded, in research reported last year, that there were at least three planets around the star. Telescopes from around the world then also observed Trappist-1 as did the Spitzer Space Telescope of NASA.
All seven are very close to the dwarf star, circling more quickly than the planets in our solar system. The innermost completes an orbit in just 1.5 days. The farthest one completes an orbit in about 20 days. That makes the planetary system more like the moons of Jupiter than a larger planetary system like our solar system.
“They form a very compact system,” Dr. Gillon, of the University of Liege, said, “the planets being pulled close to each other and very close to the star.”
In addition, the orbital periods of the inner six suggest that the planets formed farther away from the star and then were all gradually pulled inward, Dr. Gillon said.
Because the planets are so close to a cool star, their surfaces could be at the right temperatures to have water flow, considered one of the essential ingredients for life.
The fourth, fifth and six planets orbit in the star’s “habitable zone,” where the planets could sport oceans. So far that is just speculation, but by measuring which wavelengths of light are blocked by the planet, scientists will be able to figure out what gases float in the atmospheres of the seven planets.
So far, they have confirmed for the two innermost planets that they are not enveloped in hydrogen. That means they are rocky like Earth, ruling out the possibility that they were mini-Neptune gas planets that are prevalent around many other stars.
Because the planets are so close to Trappist-1, they have quite likely become “gravitationally locked” to the star, always with one side of the planets facing the star, much as it is always the same side of Earth’s moon facing Earth. That would mean one side would be warmer, but an atmosphere would distribute heat, and the scientists said that would not be an insurmountable obstacle for life.
As with the previous announcements regarding Earth-like exoplanets found around other stars both near and far, it’s important to note what this announcement does not mean. So far, there is not sufficient evidence to say whether there is evidence that conditions exist on any of these planets that would make it possible for life as we know and understand it to arise in even its simplest forms. We’re also quite far away from being able to say definitively that this is evidence of any form of life, not to mention any evidence of intelligent life of any kind. Indeed, given the limitations of technology and the distance between here and there, the odds that we’d be able to definitively reach that conclusion any time soon are fairly low. What we are able to say, though, is that we’ve found further evidence that the existence of Earth-like exoplanets elsewhere in the Milky Way Galaxy establishes that our planet is not so unique as to make it impossible that life could have arisen elsewhere at some point in time, or that it hasn’t done so already. That alone is a profound conclusion because it wasn’t so long ago that we couldn’t say for sure that planetary systems resembling our Solar System were a common occurrence at all, never mind that there could be planets like Earth elsewhere in the universe. At this point, in fact, it seems as though we can say for sure that our planet isn’t unique in the galaxy and that the odds are that there are far more planets like this elsewhere, not only in our galaxy but also elsewhere in the vastness of the universe.
As noted, the next step in the process for the scientists working on these discoveries will be an attempt to determine if the conditions for life can be confirmed on any of these planets. This will come when the James Webb Telescope is launched into orbit in October 2018. This telescope will go far beyond the capabilities of the Hubble and Keppler Telescopes in that it will be able to use advanced equipment to measure light emissions from the planets to determine the composition of their atmospheres. If evidence of the gasses known to be essential to be life as we know it are found, then that will be yet further confirmation of their Earth-like status and raises the exciting potential that we’ve discovered evidence of life itself, although that will be far more difficult to determine. Ultimately, that determination could end up being as much guesswork as anything else, but it would nonetheless be a revolutionary finding that will change our ideas of just how abundant life in some form could be in the universe as a whole.
This discovery also emphasizes the importance of a point that I’ve made in the past, namely the idea that NASA and our space program is far more successful than some critics have lamented in recent years. With the retirement of the Space Shuttle and the end, for now, of America launching its own manned missions to space, many critics have claimed that NASA has lost focus and that the United States has essentially given up when it comes to having a credible space program. That claim is obviously without merit. For one thing, while we are currently reliant on Russia to get astronauts to and from the International Space Station, research and testing on a new generation of manned space vehicles by NASA and various private initiatives such as SpaceX is well underway, and it is projected that we’re only a few years away from the U.S. being able to get astronauts to the ISS on its own. Additionally, there are plans for a return to the Moon in the very near future as part of a longer-term project that has a mission to Mars as the ultimate target. Finally, while all of this is going on we have the successes of the unmanned program to point to as evidence of just how successful our space program has been over the past several years. Just in the past several years, we’ve seen fly-by missions to Pluto, Saturn, Jupiter, and the Asteroid Belt, ongoing rovers on the surface of Mars that continue to return data to Earth on a nearly daily basis, two probes (Voyager I and II) that have essentially departed the Solar System, and now these discoveries which are arguably more profound than simply launching a few guys to the International Space Station and then returning them three to six months later. That doesn’t sound like a “dead” space program to me, it sounds like to me like one that is very much alive and well and expanding human knowledge on a daily basis.
Illustration via NASA and JPL