This month, a new chapter in the search for extraterrestrial life will open, when the most powerful space telescope ever built will begin spying on planets orbiting other stars. Astronomers hope that the James Webb Space Telescope will reveal whether some of these planets have atmospheres that could support life.
The detection of an atmosphere in another solar system would be quite remarkable. But there’s a chance, even a small one, that one of those atmospheres will deliver what’s known as a biosignature: a signal of life itself.
“I think we’re going to 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 be able to detect life right away.”
So far, Earth remains the only planet in the universe where life exists. Scientists have been sending probes to Mars for nearly 60 years and still haven’t found Martians. But it’s conceivable that life is lurking beneath the surface of the Red Planet, or waiting to be discovered on a moon of Jupiter or Saturn. Some scientists hoped so VenusDespite the scorching atmosphere of sulfur dioxide clouds, it may be home to Venusians.
Even if Earth is the only planet in our solar system that harbors life, many other solar systems in the universe harbor so-called exoplanets.
In 1995, Swiss astronomers observed the first exoplanet orbiting a sun-like star. The exoplanet known as 51 Pegasi b proved to be an unpromising home for life — a bloated gas giant larger than Jupiter and a roasting 1,800 degrees Fahrenheit.
In later years, scientists found More than 5,000 other exoplanets. Some of them are more like Earth – about the same size, made of rock rather than gas, and orbiting their star in the “Goldilocks Zone”, not close enough to cook but not close enough to freeze.
Unfortunately, the relatively small size of these exoplanets has made their study extremely difficult until now. The James Webb Space Telescope, launched last Christmas, will act as a magnifying glass to allow astronomers to take a closer look at these worlds.
Kourou has had the telescope since its launch from French Guiana he traveled A million miles from Earth, it enters its orbit around the sun. There, a shield shields its 21-meter mirror from any heat or light from the sun or Earth. In this deep darkness, the telescope can detect faint, distant flashes of light, including new details about distant planets.
The space telescope “is the first major space observatory to consider the study of exoplanet atmospheres in its design,” said Dr. Mansfield said.
NASA engineers began taking pictures of a series of objects with the Webb telescope in mid-June and will release the first images to the public on July 12.
Eric Smith, lead scientist of the program, said that exoplanets will be in that first set of images. Since the telescope will spend relatively little time observing exoplanets, Dr. Smith considered these early images to be a “quick and dirty” look at the telescope’s power.
These quick glances will be followed by a series of longer observations starting in July that will provide a clearer picture of the exoplanets.
Several groups of astronomers plan to investigate seven planets It orbits a star called Trappist-1. Previous observations suggested that three of the planets occupy the habitable zone.
“This is 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 observe the Trappist-1 planets starting July 4.
Because Trappist-1 is a small, cool star, its habitable zone is closer to our own solar system. As a result, its potentially habitable planets orbit in close proximity, taking only a few days to orbit the star. Every time the planets pass in front of Trappist-1, scientists will be able to answer a basic but important question: Do any of them have atmospheres?
“If there’s no air, it’s impossible to live, even if it’s in the habitable zone,” said Nicole Lewis, an astronomer at Cornell University.
Dr. Lewis and other astronomers would not be surprised if they find no atmosphere surrounding Trappist-1’s planets. Even if the planets formed atmospheres when they formed, the star could have blasted them with ultraviolet and X-rays long ago.
“It’s possible that they can remove the entire atmosphere before they can start creating life on a planet,” said Dr. Mansfield said. “That’s the first-order question we’re trying to answer here: Can these planets have atmospheres long enough to support life?”
A planet passing in front of Trappist-1 will cast a small shadow, but the shadow will be too small for the space telescope to capture. Instead, the telescope will detect a slight dimming of the light from the star.
“It’s like watching a solar eclipse with your eyes closed,” said astronomer Jacob Lustig-Yaeger, who is on a postdoctoral fellowship at the Johns Hopkins Applied Physics Laboratory. “You can feel the light fading.”
A planet with an atmosphere would dim, unlike a starless planet behind it. Some of the star’s light will pass straight through the atmosphere, but gases will absorb light at certain wavelengths. If astronomers looked only at starlight at these wavelengths, the planet would darken Trappist-1 even more.
The telescope will send these observations of Trappist-1 back to Earth. “And then you get an email like, ‘Hi, your data is available,'” said Dr. Mansfield said.
But the light from Trappist-1 will be so faint that it will take time to make out. “Your eye is used to dealing with millions of photons per second,” said Dr. Smith said. “But these telescopes collect only a few photons per second.”
First Dr. Before Mansfield or his colleagues can analyze exoplanets that pass in front of Trappist-1, astronomers will first have to distinguish them from the small fluctuations caused by the telescope’s own instruments.
“A lot of what I actually do is make sure that we fine-tune all the weird things that the telescope is doing so that we can see these little signals,” said Dr. Mansfield said.
Perhaps at the end of these efforts, Dr. Mansfield and his colleagues will explore the atmosphere around the Trappist-1 planet. But this result will not only reveal the nature of the atmosphere. It can be rich in nitrogen and oxygen, like on Earth, or more like a toxic stew of carbon dioxide and sulfuric acid on Venus. Or it could be a mixture scientists haven’t 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 and simulations and all that, but we really have no idea. We have to go and see.”
The James Webb Space Telescope, sometimes called JWST, may be powerful enough to identify the specific ingredients of exoplanet atmospheres because each type of molecule absorbs different wavelengths of light.
But these discoveries will depend on the weather conditions on the exoplanets. A bright, reflective cloud cover could block any starlight from entering the exoplanet’s atmosphere, ruining attempts to find alien weather.
“It’s really hard to tell the difference between cloudy and atmospheric atmosphere,” said Dr. Rathke said.
If the weather cooperates, astronomers are especially eager to find out if exoplanets have water in their atmospheres. At least on Earth, water is an essential requirement for biology. “We think this would probably be a good starting point for looking for life,” said Dr. Mansfield said.
But a watery atmosphere does not necessarily mean life on an exoplanet. To be sure that a planet is alive, scientists will need to detect a biosignature, a molecule or combination of molecules, that is made differently by the organisms.
Scientists are still debating what constitutes a valid biosignature. Earth’s atmosphere is unique in our solar system in that it contains a lot of oxygen, mostly the product of plants and algae. But oxygen can also be produced without the help of life, when water molecules in the air break down. Methane can also be released by living microbes as well as volcanoes.
It is possible that there is a special balance of gases that can provide a distinct biosignature that cannot be maintained without the help of life.
“We need extremely favorable scenarios to find these biosignatures,” said Dr. Rathcke. “I’m not saying it’s impossible. I think it’s just too far. We should be very lucky.”
Finding such a balance may require the Webb telescope to observe the planet as it passes in front of Trappist-1 multiple times, said Joshua Krissansen-Totton, a planetary scientist at the University of California, Santa Cruz.
“If someone comes forward in the next five years and says, ‘Yes, we found life with JWST,’ I would be very skeptical of that claim,” said Dr. Krissansen-Totton said
It is possible that the James Webb Space Telescope will not be able to find biosignatures. That task may have to wait for the next generation of space telescopes, more than a decade away. These will study exoplanets the same way people look at Mars or Venus in the night sky: by observing the starlight that reflects them against the black background of space, rather than observing them as they pass in front of the star.
“Basically, we will be doing very important groundwork for future telescopes,” said Dr. Rathcke predicted. “I would be very surprised if JWST provided biosignature detections, but I hope to continue with the corrections. I mean, that’s basically what I do this for. “
