An international team of researchers has used the NASA/ESA/CSA James Webb Space Telescope to measure the temperature of the rocky exoplanet TRAPPIST-1 b. The measurement is based on the planet’s thermal emission: heat energy given off in the form of infrared light detected by Webb’s Mid-Infrared Instrument (MIRI). The result indicates that the planet’s dayside has a temperature of about 500 kelvins (roughly 230°C), and suggests that it has no significant atmosphere. This is the first detection of any form of light emitted by an exoplanet as small and as cool as the rocky planets in our own solar system. The result marks an important step in determining whether planets orbiting small active stars like TRAPPIST-1 can sustain atmospheres needed to support life. It also bodes well for Webb’s ability to characterise temperate, Earth-sized exoplanets using MIRI.

“These observations really take advantage of Webb’s mid-infrared capability,” said Thomas Greene, an astrophysicist at NASA’s Ames Research Center and lead author on the study published today in the journal Nature. “No previous telescopes have had the sensitivity to measure such dim mid-infrared light.”

Rocky planets orbiting ultra cool red dwarfs

In early 2017, astronomers reported the discovery of seven rocky planets orbiting an ultracool red dwarf star (or M dwarf) 40 light-years from Earth. What is remarkable about the planets is their similarity in size and mass to the inner, rocky planets of our own solar system. Although they all orbit much closer to their star than any of our planets orbit the Sun – all could fit comfortably within the orbit of Mercury – they receive comparable amounts of energy from their tiny star.

TRAPPIST-1 b, the innermost planet, has an orbital distance about one hundredth that of Earth’s and receives about four times the amount of energy that Earth gets from the Sun. Although it is not within the system’s habitable zone, observations of the planet can provide important information about its sibling planets, as well as those of other M-dwarf systems.

“There are ten times as many of these stars in the Milky Way as there are stars like the Sun, and they are twice as likely to have rocky planets as stars like the Sun,” explained Greene. “But they are also very active – they are very bright when they’re young and they give off flares and X-rays that can wipe out an atmosphere.”

Co-author Elsa Ducrot from CEA in France, who was on the team that conducted the initial studies of the TRAPPIST-1 system, added, “It’s easier to characterise terrestrial planets around smaller, cooler stars. If we want to understand habitability around M stars, the TRAPPIST-1 system is a great laboratory. These are the best targets we have for looking at the atmospheres of rocky planets.”

Detecting an atmosphere (or not)

Previous observations of TRAPPIST-1 b with the NASA/ESA Hubble Space Telescope, as well as NASA’s Spitzer Space Telescope, found no evidence for a puffy atmosphere, but were not able to rule out a dense one.

One way to reduce the uncertainty is to measure the planet’s temperature. “This planet is tidally locked, with one side facing the star at all times and the other in permanent darkness,” said Pierre-Olivier Lagage from CEA, a co-author on the paper. “If it has an atmosphere to circulate and redistribute the heat, the dayside will be cooler than if there is no atmosphere.”

The team used a technique called secondary eclipse photometry, in which MIRI measured the change in brightness from the system as the planet moved behind the star. Although TRAPPIST-1 b is not hot enough to give off its own visible light, it does have an infrared glow. By subtracting the brightness of the star on its own (during the secondary eclipse) from the brightness of the star and planet combined, they were able to successfully calculate how much infrared light is being given off by the planet.

Measuring minuscule changes in brightness

Webb’s detection of a secondary eclipse is itself a major milestone. With the star more than 1,000 times brighter than the planet, the change in brightness is less than 0.1%.

“There was also some fear that we’d miss the eclipse. The planets all tug on each other, so the orbits are not perfect,” said Taylor Bell, the post-doctoral researcher at the Bay Area Environmental Research Institute who analysed the data. “But it was just amazing: The time of the eclipse that we saw in the data matched the predicted time within a couple of minutes.”

Analysis of data from five separate secondary eclipse observations indicates that TRAPPIST-1 b has a dayside temperature of about 500 kelvins, or roughly 230°C. The team thinks the most likely interpretation is that the planet does not have an atmosphere.

“We compared the results to computer models showing what the temperature should be in different scenarios,” explained Ducrot. “The results are almost perfectly consistent with a blackbody made of bare rock and no atmosphere to circulate the heat. We also didn’t see any signs of light being absorbed by carbon dioxide, which would be apparent in these measurements.”

This research was conducted as part of Guaranteed Time Observation (GTO) program 1177, which is one of eight approved GTO and General Observer (GO) programs designed to help fully characterise the TRAPPIST-1 system. Additional secondary eclipse observations of TRAPPIST-1 b are currently in progress, and now that they know how good the data can be, the team hopes to eventually capture a full phase curve showing the change in brightness over the entire orbit. This will allow them to see how the temperature changes from the day to the nightside and confirm if the planet has an atmosphere or not.

“There was one target that I dreamed of having,” said Lagage, who worked on the development of the MIRI instrument for more than two decades. “And it was this one. This is the first time we can detect the emission from a rocky, temperate planet. It’s a really important step in the story of discovering exoplanets.”

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This is not a true planetary alignment where they will appear in a straight line, but NASA scientist Bill Cooke told CBS News that the planets will be visible on March 28 and that the “alignment: will look “very pretty.”

How to watch the 5 planets

While the five planets should technically be visible along with the waxing crescent moon in most parts of the world, you will not be able to see it unless you are in a location with an unobstructed view of the horizon.

According to Rick Feinberg, senior contributing editor at Sky & Telescope magazine, Venus and Mars should be easy to spot. Venus is the brightest planet in the solar system and will be high in the sky, and Mars will shine brightly next to the waxing Moon. But on the other hand, Uranus, which will appear near Venus, will appear faint and will only be visible next.

“Wait until the sun has set and then go out and look low in that bright part of the sky where the sun has just set with binoculars, and you should see brighter Jupiter next to fainter Mercury,” said Fienberg to NPR.

In order to get the best view of this rare celestial event, go to a location with as little light pollution as possible and a clear horizon with not obstructions. Once there, you should be able to spot most planets, apart from Jupiter and Mercury, without the use of binoculars.

Is this a rare event?

While tonight is not an everyday event, it is not truly a five-planet alignment since the planets will not appear as if they form a single straight line.

If you were looking for an actual alignment of five planets, that time has passed. A true 5 planet alignment happened in June last year when Mercury, Venus, Mars, Jupiter and Saturn stretched across the sky from low in the east to higher in the south in the order of their distance from the Sun.

Even discounting the rare coincidence where they appeared in that particular order, the planetary alignment in June was the first one in nearly eighteen years, with the last time being on December 2004. Such an event is not expected to happen again until 2040, according to NPR.

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MOSCOW –

A Russian space capsule safely returned to Earth without a crew Tuesday, months after it suffered a coolant leak in orbit.

The Soyuz MS-22 leaked coolant in December while attached to the International Space Station. Russian space officials blamed the leak on a tiny meteoroid that punctured the craft’s external radiator. They launched an empty replacement capsule last month to serve as a lifeboat for the crew.

The damaged capsule safely landed Tuesday under a striped parachute in the steppes of Kazakhstan, touching down as scheduled at 5:45 p.m. (7:45 a.m. EDT) 147 kilometres (91 miles) southeast of Zhezkazgan under clear blue skies.

Space officials determined it would be too risky to bring NASA’s Frank Rubio and Russia’s Sergey Prokopyev and Dmitri Petelin back in the Soyuz in March as originally planned, as cabin temperatures would spike with no coolant, potentially damaging computers and other equipment, and exposing the suited-up crew to excessive heat.

The three launched in September for what should have been a six-month mission on the International Space Station. They now are scheduled to return to Earth in September in a new Soyuz that arrived at the space outpost last month with no one on board, meaning the trio will spend a year in orbit.

Also on the station are NASA astronauts Stephen Bowen and Woody Hoburg, the United Arab Emirates’ Sultan Alneyadi, and Russia’s Andrey Fedyaev.

A similar coolant leak was spotted in February on the Russian Progress MS-21 cargo ship docked at the space outpost, raising suspicions of a manufacturing flaw. Russian state space corporation Roscosmos ruled out any defects after a check and concluded that both incidents resulted from hits by meteoroids.

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