This month will mark a new chapter in the search for extraterrestrial life, when the most powerful space telescope yet built begins to spy on planets orbiting other stars. Astronomers hope that the James Webb Space Telescope will reveal whether some of these planets have atmospheres that might support life.
Determining the atmosphere in another solar system would be cool enough. But there is a chance – albeit small – that one of these atmospheres offers what is known as a biosignature: a reference to life itself.
“I think we’ll be able to find planets that we think are interesting — you know, good prospects for life,” said Megan Mansfield, an astronomer at the University of Arizona. “But we won’t necessarily be able to identify life right away.”
So far, Earth remains the only planet in the universe where life is known to exist. Scientists have been sending probes to Mars for nearly 60 years and have yet to find Mars. But it is conceivable that life is hiding beneath the surface of the red planet or waiting to be discovered on the moon of Jupiter or Saturn. Some scholars have expressed their hope for this VenusDespite the scorching atmosphere of clouds of sulfur dioxide, it may be home to the children of Venus.
Even if Earth turns out to be the only planet in our solar system that harbors life, many other solar systems in the universe hold so-called exoplanets.
In 1995, French astronomers discovered the first exoplanet orbiting a sun-like star. Known as 51 Pegasi b, the exoplanet turns out to be an unpromising home for life – a puffy gas giant larger than Jupiter, and 1800 degrees Fahrenheit warm.
In the years that followed, scientists found More than 5,000 other exoplanets. Some are very similar to Earth – roughly the same size, made of rock instead of gas and orbiting in the “Goldilocks Zone” around their star, not too close to cooking but not far enough to freeze.
Unfortunately, the relatively small size of these exoplanets has made them extremely difficult to study, until now. The James Webb Space Telescope, launched last Christmas, will change that, acting as a magnifying glass to allow astronomers to look more closely at these worlds.
Since its launch from Kourou, French Guiana, the telescope has I travelled A million miles from Earth, it enters its orbit around the Sun. There, a shield shields his 21-foot mirror from any heat or light from the sun or the ground. In this deep darkness, the telescope can detect faint, distant rays of light, including those that could reveal new details about distant planets.
Dr. Mansfield said the space telescope “is the first large space observatory to take into account the study of the atmospheres of exoplanets in its design.”
NASA engineers began taking pictures of a range of objects with the Webb Telescope in mid-June and will release their first images to the public on July 12.
The exoplanets will be in that first batch of images, Eric Smith, the program’s chief scientist, said. Since the telescope will spend a relatively short time observing the exoplanets, Dr. Smith considered those first images a “quick and dirty” look at the power of the telescope.
These quick looks will follow a series of much longer observations, starting in July, providing a clearer picture of the exoplanets.
A number of teams of astronomers plan to take a look at 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 traces 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 starting around July 4.
Since Trappist-1 is a small, cold star, its habitable zone is closer than it is in our solar system. As a result, its potentially habitable planets orbit at close range, taking only a few days to orbit the star. Each time the planets pass in front of Trappist-1, scientists will be able to address a basic but crucial question: Do any of them have an atmosphere?
“If it didn’t have air, it wouldn’t be habitable, even if it was in a habitable area,” said Nicole Lewis, an astronomer at Cornell University.
Dr. Lewis and other astronomers would not be surprised not to find atmospheres surrounding the planets Trappist-1. Even if the planets had developed atmospheres when they formed, the star may have blew them away long ago using ultraviolet and X-rays.
“It’s possible that they could strip all of a planet’s atmosphere away before it even has a chance to start creating life,” Dr. Mansfield said. “That’s the first question we’re trying to answer here: whether these planets could have an atmosphere long enough to be able to develop life.”
A planet passing in front of Trappist-1 will create a small shadow, but the shadow will be too small for a space telescope to pick up. Instead, the telescope will detect a slight dimming in the light from the star.
“It’s like looking at a solar eclipse with your eyes closed,” said Jacob Lustig-Jeiger, an astronomer who did a postdoctoral fellowship at the Johns Hopkins Laboratory of Applied Physics. “You might have some sense that the light has dimmed.”
A planet with an atmosphere would darken the star behind it differently than a naked planet. Some of the star’s light will pass directly through the atmosphere, but gases will absorb light at certain wavelengths. If astronomers only looked at starlight at those wavelengths, the planet would dim Trappist-1 even more.
The telescope will send these Trappist-1 observations back to Earth. And then you get an email like, ‘Hey, your data is available,’ Dr. Mansfield said.
But the light from Trappist-1 will be so faint that it will take time to make sense of it. “Your eye is used to dealing with millions of photons per second,” Dr. Smith said. “But these telescopes, they just collect a few photons per second.”
Before Dr. Mansfield or her fellow astronomers can analyze the exoplanets passing in front of Trappist-1, they will first have to distinguish them from the tiny fluctuations produced by the telescope’s special mechanism.
“A lot of the work I do actually is making sure that we carefully correct whatever weird things the telescope is doing, so we can see those very small signals,” Dr. Mansfield said.
At the end of these efforts, Dr. Mansfield and her colleagues may discover an atmosphere around Trappist-1. But this result alone will not reveal the nature of the atmosphere. It might be rich in nitrogen and oxygen, as it is on Earth, or akin to the toxic soup of carbon dioxide and sulfuric acid on Venus. Or it could be a combination that scientists have never seen before.
“We have no idea what these atmospheres are made of,” said Alexander Rathke, an astronomer at the Technical University of Denmark. “We have ideas and simulations and all that stuff, but we really don’t have any idea. We have to go and look.”
The James Webb Space Telescope, sometimes called the JWST, may prove powerful enough to determine the specific components of exoplanet atmospheres because each type of particle absorbs a different range of wavelengths of light.
But these discoveries will depend on the weather on the outer planets. A bright, reflective blanket of clouds could block any starlight from entering the atmosphere of an exoplanet, destroying any attempt to find space air.
“It’s really hard to distinguish between an atmosphere with clouds and without an atmosphere,” said Dr. Rathcke.
If the weather is cooperative, astronomers are especially keen to find out if exoplanets have water in their atmospheres. At least on Earth, water is a prerequisite for biology. “We think that would probably be a good starting point for the search for life,” Dr. Mansfield said.
But a watery atmosphere does not necessarily mean that an exoplanet harbors life. To be sure a planet is alive, scientists will have to discover a biomarker, a molecule, or a group of several molecules that are characteristically formed by living organisms.
Scientists are still debating what a reliable biosignature is. Earth’s atmosphere is unique in our solar system in that it contains a lot of oxygen, largely the product of plants and algae. But oxygen can also be produced without the aid of life, when water molecules in the air split. Likewise, methane can be released by living microbes but also by volcanoes.
It is possible that there is a certain balance of gases that can provide a clear vital imprint, which cannot be maintained without the help of life.
“We need very favorable scenarios to find these vital fingerprints,” said Dr. Rathcke. “I’m not saying it’s not possible. I just think it’s far-fetched. We need to be very lucky.”
Finding such a balance would require the Webb Telescope to observe a planet that frequently passes in front of Trappist-1, said Joshua Krissansen-Totton, a planetary scientist at the University of California, Santa Cruz.
“If anyone would come forward in the next five years and say, ‘Yes, we found life with JWST,’ I would be very skeptical of that claim,” said Dr. Krissansen-Totton.
It’s possible that the James Webb Space Telescope simply won’t be able to find biometrics. This mission may have to wait for the next generation of space telescopes, more than a decade later. It would study these exoplanets the same way people look at Mars or Venus in the night sky: by observing the reflection of starlight on them against the black background of space, rather than as they pass in front of a star.
“Mostly, we will make the very important foundation work for future telescopes,” Dr. Rathcke predicted. “I would be very surprised if JWST introduced biometric fingerprint detections, but I hope to stand corrected. I mean, that is basically what I’m doing this work for.”
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