Webb will take the next step in the search for habitable worlds – Spaceflight Now


Artist’s concept of the James Webb Space Telescope in its deployed configuration. Credit: ESA / ATG medialab

Starting next year, the James Webb Space Telescope will scan a sample of the nearly 5,000 alien worlds discovered around other stars to help astronomers identify which of the rocky planets may have atmospheres that could support life.

When scientists started designing Webb in the 1990s, astronomers had detected only a handful of planets outside of our solar system. Today, thanks in large part to NASA’s retired Kepler Planet Hunting Observatory, there are more than 4,800 confirmed exoplanets in the catalog.

Webb’s numerous launch delays and cost overruns culminated in the mission’s scheduled launch on Saturday from French Guiana. A European Ariane 5 rocket will send the 13,584-pound (6,161.4 kilograms) observatory into an orbit around Lagrange’s L2 point, a gravitationally neutral location four times farther from Earth than the Moon.

Astronomers designed the mission that would become Webb in 1996, when officials hoped the mission could be on the launch pad in 2007. By 2003, the launch date slipped to 2011, and then it was postponed to 2014, 2018 , 2019 and 2020.

The field of astronomy has changed since the 1990s. The construction of more powerful ground-based telescopes, and 31 years of observations with the Hubble Space Telescope, have resulted in a constant rate of discovery while Webb was stranded on planet Earth.

The search for exoplanets jumped into high gear with the launch of NASA’s Kepler Telescope in 2009. More than half of the confirmed alien worlds known today have been detected by Kepler.

“If the launch had taken place in 2011, we would have only had a handful of planets to explore,” said Néstor Espinoza, astronomer at the Space Telescope Science Institute, where Webb will be monitored after the launch. “Now we have a choice of 4,000 planets. “

The fully deployed primary mirror of the James Webb Space Telescope. Credit: NASA / Chris Gunn

Hubble’s successor Webb is the largest space telescope in history, with a primary mirror 21.3 feet (6.5 meters) in diameter. A five-layered sunshade will deploy to the size of a tennis court in the first week after launch, allowing Webb’s telescope and four science instruments to start cooling down to minus 388 degrees Fahrenheit, or 40 degrees above absolute zero.

Hubble is sensitive to cosmic light sources in the ultraviolet, visible and near infrared wavelengths. Webb will focus directly on the infrared universe, with one edge of its observation strip at the red end of the visible spectrum.

The new telescope is 100 times more powerful than Hubble. Although smaller than many ground-based observatories, Webb will hover over the scintillating effect of Earth’s atmosphere, which also absorbs a lot of the faint infrared light from stars and distant galaxies.

Mark McCaughrean, an interdisciplinary Webb scientist at the European Space Agency, said research on exoplanets is one of the key pillars of the mission, alongside finding the first galaxies in the universe and exploring the regions of star formation in our own Milky Way galaxy.

“What’s amazing about this machine is that while it wasn’t originally designed for this kind of science, it’s such a capable observatory,” said McCaughrean, who has worked on the Webb mission since. 1998. “It has so many modes, and so many filters, so many gratings, and spectroscopy mixed with imagery, that it is a perfect machine for the next stage of studying planets around other stars and of the measurement of their atmosphere.

Webb, with a relatively narrow field of view, will not seek to add to the list of confirmed exoplanets. Instead, it will follow discoveries made by missions like Kepler and NASA’s Transiting Exoplanet Survey satellite, launched in 2018.

The TESS mission scans the entire sky for planets around relatively bright, nearby stars – perfect candidates for Webb’s observations.

John Grunsfeld, a former astronaut, led the direction of the NASA science mission from 2012 to 2016. In this capacity, he oversaw the selection of the TESS mission through a competition with other proposals from astronomy for agency funding.

“I chose the Transiting Exoplanet Survey satellite, in part because it would find targets for the James Webb Space Telescope,” Grunsfeld said. “So now we have a catalog of exoplanets in transit nearby that James Webb can query.”

Four planets more massive than Jupiter can be seen orbiting the young star HR 8799 in a composite of images captured by the WM Keck ground observatory. Credit: NASA / Jason Wang and Herzberg Institute of Astrophysics / Christian Marois

“We know, basically, if you look at the night sky, every star is surrounded by a solar system,” Grunsfeld said.

Webb is expected to begin scientific operations six months after launch, and one of the new observatory’s priority targets will be the TRAPPIST-1 planetary system 39 light-years away, home to at least seven rocky worlds confirmed to be roughly the size of the Earth. Three of the planets orbit their host star, a red dwarf smaller than the sun, in the so-called habitable zone, where liquid water could be present.

With Webb, astronomers will watch the planets pass by their mother stars. The transits temporarily prevent some of the star’s light from reaching the telescope.

“Some of the starlight will pass through the atmosphere of this planet on its way to our telescope,” said John Mather, senior scientist for Project Webb at NASA’s Goddard Space Flight Center in Maryland. “We can analyze this atmosphere, if there is one, and say what is in it.”

“You will be able to detect things like water, carbon dioxide, ozone on these planets,” Espinoza said.

Webb’s instruments will split starlight into spectra, much like a raindrop does with sunlight. Other telescopes have used the same technique to measure the composition of the atmospheres of giant gas planets, similar to Jupiter or Neptune.

Astronomers will employ Webb to do the same for smaller planets with solid surfaces like Earth’s.

“Some are temperate, and a big question is whether any of them have atmospheres,” said Klaus Pontoppidan, Project Webb scientist at the Space Telescope Science Institute.

Water, in particular, could be detectable in the atmospheres of exoplanets with a huge infrared telescope like Webb. If they don’t have an atmosphere, perhaps Webb could educate scientists on the makeup of the rocky surfaces of planets – a kind of long-range geology, Espinoza said.

This artist’s concept shows what each of the TRAPPIST-1 planets can look like, based on available data on their orbital sizes, masses and distances. Credit: NASA / JPL-Caltech

Webb also has the sensitivity to directly image Neptune-sized planets around other stars, according to Espinoza. Current observatories can image planets the size of Jupiter.

The transit observation method captures only a small fraction of the exoplanets that orbit their star on a path aligned with our solar system. But the method allows scientists to use starlight to uncover details about planetary atmospheres.

“Until recently, the only known planetary system was our own solar system,” said Antonella Nota, scientist with ESA’s Webb project.

“Are we alone? Is Earth unique? Do we have other planets that can host life? (These are) very ambitious questions that challenge us all. So Webb studies the atmospheres of these exoplanets in detail.

Closer to home, Webb will point to the moon of Jupiter Europa, which has a global ocean of liquid water buried under an icy crust. Webb could confirm a tentative Hubble detection of water plumes bursting through Europe’s ice shell.

Remote observations with Webb will help scientists prepare for the arrival of NASA’s Europa Clipper mission to Jupiter. This robotic probe is slated for launch in 2024 and will repeatedly fly over Europa with a sophisticated instrument suite to study the moon’s geology and environment.

Webb will also collect data on the climate of Mars, the structure and moons of Uranus and Neptune, and the population of miniature worlds frozen in the Kuiper Belt at the outer border of our solar system.

“It’s been a long road to get to where we are at,” said Heidi Hammel, Webb interdisciplinary scientist at the Association of Universities for Research in Astronomy. “Even so, we planned a telescope so revolutionary that it withstood the test of that time.”

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