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NGC 346, one of the most dynamic star-forming regions in nearby galaxies, is full of mystery; now, though, it is less mysterious thanks to new findings from the NASA/ESA/CSA James Webb Space Telescope.

NGC 346 is located in the Small Magellanic Cloud (SMC), a dwarf galaxy close to our Milky Way. The SMC contains lower concentrations of elements heavier than hydrogen or helium, which astronomers call metals, than seen in the Milky Way. Since dust grains in space are composed mostly of metals, scientists expected that there would only be small amounts of dust, and that it would be hard to detect. But new data from Webb reveals just the opposite.

Webb Inspects NGC 346 (NIRCam Image) — This image features NGC 346, one of the most dynamic star-forming regions in nearby galaxies, as seen by the NASA/ESA/CSA James Webb Space Telescope.
NCG 346 is located in the Small Magellanic Cloud (SMC), a dwarf galaxy close to our Milky Way.
Credit:
NASA, ESA, CSA, STScI, A. Pagan (STScI)

Astronomers probed this region because the conditions and amount of metals within the SMC resemble those seen in galaxies billions of years ago, during an era in the Universe’s history known as ‘cosmic noon,’ when star formation was at its peak. Some 2 to 3 billion years after the Big Bang, galaxies were forming stars at a furious rate. The fireworks of star formation happening then still shape the galaxies we see around us today.

“A galaxy during cosmic noon wouldn’t have one NGC 346, as the Small Magellanic Cloud does; it would have thousands”, said Margaret Meixner, an astronomer at the Universities Space Research Association and principal investigator of the research team. “But even if NGC 346 is now the one and only massive cluster furiously forming stars in its galaxy, it offers us a great opportunity to probe the conditions that were in place at cosmic noon.”

By observing protostars still in the process of forming, researchers can learn if the star formation process in the SMC is different from what we observe in our own Milky Way. Previous infrared studies of NGC 346 have focused on protostars heavier than about five to eight times the mass of our Sun.

“With Webb, we can probe down to lighter-weight protostars, as small as one tenth of our Sun, to see if their formation process is affected by the lower metal content,” said Olivia Jones of the United Kingdom Astronomy Technology Centre, at the Royal Observatory Edinburgh, a co-investigator on the program.

As stars form, they gather gas and dust, which can look like ribbons in Webb imagery, from the surrounding molecular cloud. The material collects into an accretion disc that feeds the central protostar. Astronomers have detected gas around protostars within NGC 346, but Webb’s near-infrared observations mark the first time they have also detected dust in these discs.

“We’re seeing the building blocks, not only of stars, but also potentially of planets,” said Guido De Marchi of the European Space Agency, a co-investigator on the research team. “And since the Small Magellanic Cloud has a similar environment to that of galaxies during cosmic noon, it’s possible that rocky planets could have formed earlier in the history of the Universe than we might have thought.”

The team also has spectroscopic observations from Webb’s NIRSpec instrument that they are continuing to analyse. These data are expected to provide new insights into the material accreting onto individual protostars, as well as the environment immediately surrounding the protostars.

These results are being presented on 11 January 2023 in a press conference at the 241st meeting of the American Astronomical Society. The observations were obtained as part of program 1227.

Webb Inspects NGC 346 (Annotated) — This image features NGC 346, one of the most dynamic star-forming regions in nearby galaxies, as seen by the NASA/ESA/CSA James Webb Space Telescope.
NCG 346 is located in the Small Magellanic Cloud (SMC), a dwarf galaxy close to our Milky Way.
Credit:
NASA, ESA, CSA, STScI, A Pagan (STScI)

Press release from ESA Webb

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Researchers have confirmed the presence of an exoplanet, a planet that orbits another star, using the NASA/ESA/CSA James Webb Space Telescope for the first time: formally classified as LHS 475 b, the planet is almost exactly the same size as our own, clocking in at 99% of Earth’s diameter.

The research team is led by Kevin Stevenson and Jacob Lustig-Yaeger, both of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. The team chose to observe this target with Webb after carefully reviewing data from NASA’s Transiting Exoplanet Survey Satellite (TESS) which hinted at the planet’s existence. Webb’s Near-Infrared Spectrograph (NIRSpec) captured the planet easily and clearly with only two transit observations.

“There is no question that the planet is there. Webb’s pristine data validate it,” said Lustig-Yaeger. “The fact that it is also a small, rocky planet is impressive for the observatory,” Stevenson added.

“These first observational results from an Earth-sized, rocky planet open the door to many future possibilities for studying rocky planet atmospheres with Webb,” agreed Mark Clampin, Astrophysics Division director at NASA Headquarters in Washington. “Webb is bringing us closer and closer to a new understanding of Earth-like worlds outside the Solar System, and the mission is only just getting started.”

Exoplanet LHS 475 b (Illustration) — Based on new evidence from the NASA/ESA/CSA James Webb Space Telescope, this illustration shows the exoplanet LHS 475 b. It is rocky and almost precisely the same size as Earth. The planet whips around its star in just two days, far faster than any planet in the Solar System. Researchers will follow up this summer with additional observations with Webb, which they hope will allow them to definitively conclude if the planet has an atmosphere. LHS 475 b is relatively close, 41 light-years away, in the constellation Octans.
Credit:
NASA, ESA, CSA, L. Hustak (STScI)

Among all operating telescopes, only Webb is capable of characterising the atmospheres of Earth-sized exoplanets. The team attempted to assess what is in the planet’s atmosphere by analysing its transmission spectrum. Although the data show that this is an Earth-sized terrestrial planet, they do not yet know if it has an atmosphere.

“The observatory’s data are beautiful,” said Erin May, also of the Johns Hopkins University Applied Physics Laboratory. “The telescope is so sensitive that it can easily detect a range of molecules, but we can’t yet draw any definitive conclusions about the planet’s atmosphere.”

Although the team can’t conclude what is present, they can definitely say what is not present.

“There are some terrestrial-type atmospheres that we can rule out,” explained Lustig-Yaeger. “It can’t have a thick methane-dominated atmosphere, similar to that of Saturn’s moon Titan.”

The team also notes that while it’s possible the planet has no atmosphere, there are some atmospheric compositions that have not been ruled out, such as a pure carbon dioxide atmosphere.

“Counterintuitively, a 100% carbon dioxide atmosphere is so much more compact that it becomes very challenging to detect,” said Lustig-Yaeger.

Exoplanet LHS 475 b — How do researchers spot a distant planet? By observing the changes in light as it orbits its star. A light curve from the NASA/ESA/CSA James Webb Space Telescope’s Near-Infrared Spectrograph (NIRSpec) shows the change in brightness from the LHS 475 star system over time as the planet transited the star on 31 August 2022. LHS 475 b is a rocky, Earth-sized exoplanet that orbits a red dwarf star roughly 41 light-years away, in the constellation Octans. The planet is extremely close to its star, completing one orbit in two Earth-days. Confirmation of the presence of the planet was made possible by Webb’s data. Credit: NASA, ESA, CSA, L. Hustak (STScI), K. Stevenson, J. Lustig-Yaeger, E. May (Johns Hopkins University Applied Physics Laboratory), G. Fu (Johns Hopkins University), and S. Moran (University of Arizona)

Even more precise measurements are required for the team to distinguish a pure carbon dioxide atmosphere from no atmosphere at all. The researchers are scheduled to obtain additional spectra with further observations this summer.

Webb also revealed that the planet is a few hundred degrees warmer than Earth, so if clouds are detected it may lead the researchers to conclude that the planet is more like Venus, which has a carbon dioxide atmosphere and is perpetually shrouded in thick cloud.

“We’re at the forefront of studying small, rocky exoplanets,” Lustig-Yaeger said. “We have barely begun scratching the surface of what their atmospheres might be like.”

The researchers also confirmed that the planet completes an orbit in just two days, information that was almost instantaneously revealed by Webb’s precise light curve. Although LHS 475 b is closer to its star than any planet in the Solar System, its red dwarf star is less than half the temperature of the Sun, so the researchers project it still could support an atmosphere.

A flat line in a transmission spectrum, like this one, can be exciting — it can tell us a lot about the planet. Researchers used the NASA/ESA/CSA James Webb Space Telescope’s Near-Infrared Spectrograph (NIRSpec) to observe exoplanet LHS 475 b on 31 August 2022. As this spectrum shows, Webb did not observe a detectable quantity of any element or molecule. The data (white dots) are consistent with a featureless spectrum representative of a planet that has no atmosphere (yellow line). The purple line represents a pure carbon dioxide atmosphere and is indistinguishable from a flat line at the current level of precision. The green line represents a pure methane atmosphere, which is not favoured since methane, if present, would be expected to block more starlight at 3.3 microns.
Credit:
NASA, ESA, CSA, L. Hustak (STScI), K. Stevenson, J. Lustig-Yaeger, E. May (Johns Hopkins University Applied Physics Laboratory), G. Fu (Johns Hopkins University), and S. Moran (University of Arizona)

The researchers’ findings have opened up the possibility of pinpointing Earth-sized planets orbiting smaller red dwarf stars.

“This rocky planet confirmation highlights the precision of the mission’s instruments,” Stevenson said. “And it is only the first of many discoveries that it will make.” Lustig-Yaeger agreed: “With this telescope, rocky exoplanets are the new frontier.”

LHS 475 b is relatively close, at only 41 light-years away, in the constellation Octans.

The team’s results were presented at a press conference of the American Astronomical Society (AAS) on Wednesday 11 January, 2023.

Webb Confirms Its First Exoplanet, LHS 475 b — Based on new evidence from the NASA/ESA/CSA James Webb Space Telescope, this illustration reflects the conclusion that the exoplanet LHS 475 b is rocky and almost precisely the same size as Earth. The planet whips around its star in just two days, far faster than any planet in the Solar System. Researchers will follow up this summer with additional observations with Webb, which they hope will allow them to definitively conclude if the planet has an atmosphere. LHS 475 b is relatively close, 41 light-years away, in the constellation Octans.
Credit:
NASA, ESA, CSA, L. Hustak (STScI)

Press release from ESA Webb

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