Next week, NASA will launch its new exoplanet hunter: a satellite that will look to the cosmos in search of worlds never before seen. Known as TESS, the spacecraft has the task of looking for planets that surround the stars outside of our Solar System to help scientists discover what these planets are made of and if any of them can sustain life.
TESS will launch on April 16, just when the old NASA exoplanet hunter is about to hang his hat. The agency's Kepler spacecraft, which was launched in 2009, will run out of fuel at some point during the next few months. But TESS has a different mission from its predecessor. Kepler's goal was simply to find as many exoplanets as possible; TESS will be more demanding, looking for planets around the stars closest to Earth. These worlds will be much easier to study since their stars will be brighter, according to NASA.
"TESS is really optimized to knock on the doors of the neighborhood and say: 'Hi, how are you?'
"Kepler had to do with a census: how common are the planets in general? How is the size distribution of the planets? Are planets the size of the Earth common?" Stephen Rinehart, the project scientist for TESS at NASA, he tells The Verge. "TESS is really optimized to knock on the doors of the neighborhood and say, 'Hi, how are you doing, what's this planet really like? & # 39;
And a particular planet type is on TESS's wish list: rocky worlds the size of Earth that are in the correct orbit around their stars, where liquid water can accumulate. If it were discovered that this planet has an atmosphere similar to that of Earth, it would open the possibility that life can also survive in that world.
Why brighter is better
Kepler just looked at some small portions of the sky at once, looking upwards of 100,000 stars. TESS will observe a field of vision 400 times larger. And you can see up to 200,000 stars, maybe millions. "Having TESS in the fold is just fantastic," says Jessie Dotson, an astrophysicist at NASA's Ames Research Center and a scientist on the Kepler spacecraft project. "They are going to find planets in parts of the sky that we can not see."
"They are going to find planets in parts of the sky that we can not see."
TESS will use the same technique as Kepler to find planets. It will look for worlds as they pass in front of their host stars, in what is known as transit. Each time a planet transits, it slightly attenuates the light from its parent star long enough for an orbital telescope to measure. But TESS will target stars much closer than Kepler saw. They will only be tens or hundreds of light years away, unlike thousands of light years away, making them 30 to 100 times brighter in the sky. That will make it easier for astronomers to learn more about the planets that surround them.
An artistic representation of TESS in search of exoplanets. Image: NASA's Goddard Space Flight Center
To really know what a planet is made of, whether rocky like Earth or a gas giant like Jupiter, you need to know its density. And the best way to measure density is to observe how the planet pulls its host star. Although a planet is relatively small, it still has a gravitational influence on its star, which causes the celestial object to wobble slightly. The extent of this wobble speaks of how massive a planet is.
Brighter stars make it easier to measure this wobble fairly quickly
Brighter stars make it easier to measure this wobble rather quickly. With distant and weak stars, astronomers do not collect as much light, so it takes more time to learn how the star is shaking. For the types of stars that Kepler observed, it could take weeks or months to discover the oscillation of a star and, as a result, the composition of a nearby exoplanet. But for the bright stars that TESS will study, it could take only a few hours.
With Kepler, astronomers could only measure some stars, says Rinehart. "With TESS, it's going to be the opposite problem, it's going to be" I can do any of these objectives, which one do I want to do? & # 39;
The TESS exoplanets will find
With its four cameras, TESS will observe the same place in the sky for only 27 days at a time before moving on to the next patch. By comparison, Kepler's observations spanned months or years. Therefore, TESS will search for planets with super short orbits, which take less than a month to complete. And that limits the types of worlds that the spacecraft can find.
On the one hand, TESS will not find the exact twin of Earth. The types of habitable worlds the size of the Earth that TESS will find are those that orbit small, weak stars known as red dwarfs. This type of stars produces much less energy than our Sun. Then the planets have to embrace these stars to be considered habitable. They must be close to get enough heat to have the opportunity to hold liquid water. And that means a year for these planets to last only a dozen or more days.
An artistic representation of an exoplanet around a red dwarf star. Image: NASA Ames / SETI Institute / JPL-Caltech.
Astronomers have been particularly enthusiastic about the search for planets around red dwarfs because these stars are abundant throughout the Universe. But the mere fact of being in the so-called "habitable zone" of such a star does not mean that these worlds can harbor life. Planets that orbit near a red dwarf usually have one side that is in constant daylight, while the other experiences constant nighttime. And red dwarfs tend to burst a lot, bathing nearby planets with energetic particles. "They are not going to be like Earth, but what is so interesting is that we really do not know what we are going to find," says Sara Seager, planetary scientist at MIT and deputy director of science at TESS. Edge.
"What's so interesting is that we really do not know what we're going to find."
When NASA's next big space observatory, the James Webb Space Telescope, comes in line, astronomers will be able to observe the atmospheres of the small planets the size of the Earth that TESS finds. However, they will have to wait a bit to know what is around them. It is assumed that James Webb will not launch until 2020 at the earliest, so it will be some years until we know if these worlds have atmospheres that can support life.
Meanwhile, Seager says she is excited to find planets that are roughly two or three times the size of Earth, known as Super-Earths or mini-Neptunes. Kepler discovered that these strange intermediate planets are actually the most common worlds that exist. But we know very little about what they are made of and where they come from. When TESS finds these mini-Neptunes and their densities, astronomers can make follow-up observations with telescopes on the ground to see what's in their atmospheres. "Are they all the same? Are they all different?" She asks. "It will help us understand how they were formed."
However, before all this happens, TESS must reach orbit. The probe is scheduled to launch at 6:32 PM ET from Cape Canaveral, Florida, on top of a SpaceX Falcon 9 rocket next week. If all goes well, the spacecraft should collect data starting in June, just as Kepler begins to disconnect. As Kepler runs out of fuel, it will not be able to redirect its antenna to Earth to send its data. Neither can he use his motors to stay in position, as the solar wind will push him.
The orbit of TESS. Image: NASA / MIT
TESS will not have this fuel problem. The spacecraft will be in a super elliptical orbit around the Earth that will carry the probe as far as the distance from the Moon. This basically means that TESS will be in a strange gravitational dance with our planet and the Moon. The orbit, which will last 13.7 days, has never before been used for a spacecraft, but it is incredibly stable. So, TESS does not need a lot of fuel. "If you move away a little, the Moon tends to take you back to the orbit in which you are supposed to be," says Rinehart. "This orbit could be stable for more than 100 years."
"After TESS, we will have a complete catalog of these planets in order of priority for follow-up."
However, getting to this type of orbit is complicated. It requires a lot of energy. But TESS has one big advantage: its small size. Weighing just 800 pounds (362 kilograms), it is much smaller than many bus-sized satellites that can weigh many thousands of pounds. The spacecraft will occupy very little space in your Falcon 9, and that will make it easier for the rocket to take this spacecraft where it should go. "It's mostly empty space," says Rinehart, referring to the nose cone at the top of the rocket. "TESS is a small thing in this great fairing, we are light and we are small."
TESS is scheduled to do science for two years when it is in space, but engineers are already planning how to extend the mission of the spacecraft. If so, this small probe could create a new exhaustive index of exoplanets that astronomers will study in the coming years. "People love planets … and the fact that they seem to come in all sizes, masses and orbits," says Seager. "Now, after TESS, we will have a complete catalog of these planets in order of priority for follow-up."