This month will mark a new chapter in the search for extraterrestrial life when the most powerful space telescope ever built begins spying on planets orbiting other stars. Astronomers hope the James Webb Space Telescope will show whether some of these planets harbor atmospheres that could support life.
Identifying an atmosphere in another solar system would be remarkable enough. But there’s even a chance – albeit tiny – that one of these atmospheres has what’s called a biosignature: a signal from life itself.
“I think we’ll be able to find planets that we think are interesting — you know, good possibilities for life,” said Megan Mansfield, an astronomer at the University of Arizona. “But we won’t necessarily be able to identify life immediately.”
So far, Earth is the only planet in the universe known to have life. Scientists have been sending probes to Mars for almost 60 years and have yet to find any Martians. But it’s conceivable that life might be hiding beneath the Red Planet’s surface or waiting to be discovered on a moon of Jupiter or Saturn. Some scientists even hope so Venuscould be home to Venusians despite its scorching atmosphere of sulfur dioxide clouds.
Even if Earth turns out to be the only planet that supports life in our own solar system, there are so-called exoplanets in many other solar systems in the universe.
In 1995, Swiss astronomers discovered the first exoplanet orbiting a sun-like star. The exoplanet known as 51 Pegasi b turned out to be an unpromising home for life – a bloated gas giant larger than Jupiter and a comfortable 1,800 degrees Fahrenheit.
In the years since, scientists have figured out more than 5,000 other exoplanets. Some of them are much more Earth-like — about the same size, rocky rather than gaseous, and orbit their star in a “Goldilocks zone,” not close enough to be boiled but not close enough to be frozen.
Unfortunately, the relatively small size of these exoplanets has made them extremely difficult to study. The James Webb Space Telescope, launched last Christmas, will change that, acting as a magnifying glass allowing astronomers to take a closer look at these worlds.
Since its launch from Kourou, French Guiana, the telescope has travelled a million miles from Earth and enters its own orbit around the Sun. There a shield protects its 21-foot mirror from any heat or light from the sun or the earth. In this deep darkness, the telescope can see faint, distant glimmers of light, including those that could reveal new details about distant planets.
The space telescope “is the first major space observatory to incorporate the study of the atmosphere of exoplanets into its design,” said Dr. said Mansfield.
NASA engineers began capturing images of a number of objects with the Webb telescope in mid-June and will release their first images to the public on July 12.
Exoplanets will feature in this first set of images, said Eric Smith, the program’s lead scientist. Because the telescope will spend relatively little time observing the exoplanets, Dr. Smith viewed these first images as a “quick and dirty” look at the telescope’s performance.
These brief glimpses will be followed by a series of much longer observations beginning in July that will provide a much clearer picture of the exoplanets.
A number of teams of astronomers plan to study it seven planets orbiting a star called Trappist-1. Previous observations indicated that three of the planets occupy the habitable zone.
“It’s an ideal place to look for signs of life outside the solar system,” said Olivia Lim, a graduate student at the University of Montreal who will be observing the Trappist 1 planets from around July 4.
Because Trappist-1 is a small, cool star, its habitable zone is closer to it than in our own solar system. As a result, its potentially habitable planets orbit the star at close range, taking only a few days to orbit the star. Each time the planets pass in front of Trappist-1, scientists can address a fundamental but crucial question: do any of them have an atmosphere?
“If it doesn’t have air, it’s not habitable, even if it’s in the habitable zone,” said Nikole Lewis, an astronomer at Cornell University.
DR. Lewis and other astronomers would not be surprised to find no atmospheres around the Trappist-1 planets. Even if the planets developed atmospheres as they formed, the star could have blasted them away with ultraviolet and X-rays long ago.
“It’s possible that they could just remove all of the atmosphere on a planet before it even had a chance to even begin forming life,” said Dr. said Mansfield. “That’s the first question we’re trying to answer here: whether these planets could have had an atmosphere long enough for life to develop.”
A planet passing in front of Trappist-1 casts a tiny shadow, but the shadow is too small for the space telescope to see. Instead, the telescope sees a slight fading of the light emanating from the star.
“It’s like looking at a solar eclipse with your eyes closed,” said Jacob Lustig-Yaeger, an astronomer who is doing a postdoctoral fellowship at the Johns Hopkins Applied Physics Laboratory. “You may feel that the light is dim.”
A planet with an atmosphere would darken the star behind it differently than a bare planet. Some of the star’s light goes directly through the atmosphere, but the gases absorb light at certain wavelengths. If astronomers only look at starlight at these wavelengths, the planet Trappist-1 will eclipse even more.
The telescope will send these observations back to Earth from Trappist-1. “And then you get an email saying, ‘Hello, your dates are available,'” says Dr. said Mansfield.
But the light coming from Trappist-1 will be so faint that it will take time to understand. “Your eye is used to dealing with millions of photons per second,” says Dr. said Smith. “But these telescopes only collect a few photons per second.”
before dr Mansfield or her fellow astronomers will be able to analyze exoplanets passing in front of Trappist-1, they must first distinguish them from tiny fluctuations generated by the telescope’s own machinery.
“A lot of the work that I actually do is making sure that we carefully correct for everything that’s weird that the telescope is doing so we can see these tiny little signals,” said Dr. said Mansfield.
It is possible that at the end of this effort, Dr. Mansfield and her colleagues will discover an atmosphere around a Trappist 1 planet. But this result alone will not reveal the nature of the atmosphere. It could be rich in nitrogen and oxygen, like on Earth, or more like Venus’s toxic stew of carbon dioxide and sulfuric acid. Or it could be a mix that scientists have never seen before.
“We have no idea what these atmospheres are made of,” said Alexander Rathcke, an astronomer at the Technical University of Denmark. “We have ideas, simulations and all that stuff, but we really have no idea. We have to go and see.”
The James Webb Space Telescope, sometimes referred to as the JWST, could prove powerful enough to determine the specific components of exoplanets’ atmospheres, since each type of molecule absorbs a different range of wavelengths of light.
But these discoveries will depend on the weather on the exoplanets. A bright, reflective cloud cover could prevent starlight from entering an exoplanet’s atmosphere and ruin any attempt to find alien air.
“It’s really hard to distinguish between an atmosphere with clouds and no atmosphere,” says Dr. said Rathcke.
If the weather cooperates, astronomers are particularly curious to see if the exoplanets have water in their atmospheres. At least on Earth, water is an essential requirement for biology. “We think that would probably be a good place to start looking for life,” said Dr. said Mansfield.
But a watery atmosphere doesn’t necessarily mean an exoplanet is home to life. To be certain that a planet is alive, scientists must recognize a biosignature, a molecule or combination of molecules characteristically made by living things.
Scientists are still debating what a reliable biosignature would be. The Earth’s atmosphere is unique in our solar system in that it is rich in oxygen, most of which is the product of plants and algae. However, oxygen can also be produced without life support when water molecules in the air are split. Methane can also be released by living microbes, but also by volcanoes.
It’s possible that there is a specific gas balance that can provide a unique biosignature, one that cannot be sustained without the help of life.
“We need extremely favorable scenarios to find these biosignatures,” said Dr. Rathcke. “I’m not saying it’s not possible. I just think it’s far fetched. We must be very lucky.”
Joshua Krissansen-Totton, a planetary scientist at the University of California, Santa Cruz, said the Webb Telescope may need to observe a planet repeatedly passing in front of Trappist-1 to find such an equilibrium.
“In the next five years, if someone comes forward and says, ‘Yes, we found life with JWST,’ I’m going to be very skeptical of that claim,” said Dr. said Krissansen-Totton
It’s possible that the James Webb Space Telescope simply won’t be able to find biosignatures. That task may have to wait for the next generation of space telescopes, which are more than a decade away. They will study exoplanets the same way humans look at Mars or Venus in the night sky: by observing the starlight reflecting off them against the black background of space, rather than observing them as they pass in front of a star.
“Most of the time we will do the very important basic work for future telescopes,” says Dr. Rathcke prophesied. “I would be very surprised if JWST provided biosignature detections, but I hope to be corrected. I mean, that’s basically what I do this work for.”