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 characterize 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 Ultracool 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 the French Alternative Energies and Atomic Energy Commission (CEA) in France, who was on the team that conducted earlier studies of the TRAPPIST-1 system, added, “It’s easier to characterize 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 Hubble and Spitzer space telescopes 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 analyzed 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.”

The team analyzed data from five separate secondary eclipse observations. “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 Webb Guaranteed Time Observation (GTO) program 1177, which is one of eight programs from Webb’s first year of science designed to help fully characterize 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.”

The paper, “Extreme plasticity of reproductive state in a female rodent,” which published March 27 in Current Biology, explores how traits once considered “fixed” in adult animals may become variable under specific pressures.

Though these rodents could have important military, biodetection and humanitarian uses, breeding them at high rates has been a challenge. The study’s findings are a step toward understanding their reproductive biology, and possibly breeding them more effectively — and may even have broader implications for other mammals struggling to reproduce.

“The more we start to understand the full scope of the reproductive process, the more we can start to get insight into those sorts of questions,” said Alex Ophir, associate professor of psychology at Cornell University and the study’s senior author. “The more examples of other mammals we get, the better, and these unusual examples can sometimes reveal a lot about women’s health and reproductive health.”

While other species are known to undergo reproductive suppression — such as animals who only mate in certain seasons — most do this hormonally rather than closing off their genitals as giant African pouched rats do. More study is needed to understand why these rodents possess this unusual trait.

One hypothesis is that “dominant” female pouched rats might be sending suppression signals to other females through pheromones, or scents in their urine, that cause them to close up.

“You could interpret it as manipulation by one female to get other females to stop reproducing, and in effect, they’ll often in these cases, start to contribute to the care of the dominant reproducing female,” Ophir said.

Another theory could be tied to resource competition, where too many offspring in a population limits available food resources, and reducing the number of babies born to others could mean more resources for one’s own babies, Ophir said.

In future work, Ophir plans to continue investigating how the animals’ extraordinary olfactory systems work and hopes to learn more about their unusual behaviors and anatomies.

“The fact that there is this naturally occurring ability to sort of change reproductive morphology and physiology suggests that things are probably a whole lot more plastic than we realize,” Ophir said. “If nothing else, it just provides another example that things aren’t as dogmatically simple as people think.”

This study was funded by the Army Research Office.

Based in part on carbon emissions, a new study using simulations identified two tipping points for the Greenland Ice Sheet: releasing 1000 gigatons of carbon into the atmosphere will cause the southern portion of the ice sheet to melt; about 2500 gigatons of carbon means permanent loss of nearly the entire ice sheet.

Having emitted about 500 gigatons of carbon, we’re about halfway to the first tipping point.

“The first tipping point is not far from today’s climate conditions, so we’re in danger of crossing it,” said Dennis Höning, a climate scientist at the Potsdam Institute for Climate Impact Research who led the study. “Once we start sliding, we will fall off this cliff and cannot climb back up.”

The study was published in AGU’s journal Geophysical Research Letters, which publishes short-format, high-impact research spanning the Earth and space sciences.

The Greenland Ice Sheet is already melting; between 2003 and 2016, it lost about 255 gigatons (billions of tons) of ice each year. Much of the melt to date has been in the southern part of the ice sheet. Air and water temperature, ocean currents, precipitation and other factors all determine how quickly the ice sheet melts and where it loses ice.

The complexity of how those factors influence each other, along with the long timescales scientists need to consider for melting an ice sheet of this size, make it difficult to predict how the ice sheet will respond to different climate and carbon emissions scenarios.

Previous research identified global warming of between 1 degree to 3 degrees Celsius (1.8 to 5.4 degrees Fahrenheit) as the threshold beyond which the Greenland Ice Sheet will melt irreversibly.

To more comprehensively model how the ice sheet’s response to climate could evolve over time, Höning’s new study for the first time used a complex model of the whole Earth system, which includes all the key climate feedback processes, paired with a model of ice sheet behavior. They first used simulations with constant temperatures to find equilibrium states of the ice sheet, or points where ice loss equaled ice gain. Then they ran a set of 20,000-year-long simulations with carbon emissions ranging from 0 to 4000 gigatons of carbon.

From among those simulations, the researchers derived the 1000-gigaton carbon tipping point for the melting of the southern portion of the ice sheet and the even more perilous 2,500-gigaton carbon tipping point for the disappearance of nearly the entire ice sheet.

As the ice sheet melts, its surface will be at ever-lower elevations, exposed to warmer air temperatures. Warmer air temperatures accelerate melt, making it drop and warm further. Global air temperatures have to remain elevated for hundreds of years or even longer for this feedback loop to become effective; a quick blip of 2 degrees Celsius (3.6 degrees Fahrenheit) wouldn’t trigger it, Höning said. But once the ice crosses the threshold, it would inevitably continue to melt. Even if atmospheric carbon dioxide were reduced to pre-industrial levels, it wouldn’t be enough to allow the ice sheet to regrow substantially.

“We cannot continue carbon emissions at the same rate for much longer without risking crossing the tipping points,” Höning said. “Most of the ice sheet melting won’t occur in the next decade, but it won’t be too long before we will not be able to work against it anymore.”