from the tentatively-named-Doc-Grumpy-Happy-Sleepy-Bashful-Sneezy-and-Dopey dept.
Astronomers have observed enough planetary transits to confirm the existence of seven "Earth-sized" exoplanets orbiting TRAPPIST-1, an ultra-cool (~2550 K) red dwarf star about 39.5 light years away. Three of the exoplanets are located inside the "habitable zone" of their parent star. These three orbit from 0.028 to 0.045 AU away from the star:
Astronomers using the TRAPPIST–South telescope at ESO's La Silla Observatory, the Very Large Telescope (VLT) at Paranal and the NASA Spitzer Space Telescope, as well as other telescopes around the world, have now confirmed the existence of at least seven small planets orbiting the cool red dwarf star TRAPPIST-1. All the planets, labelled TRAPPIST-1b, c, d, e, f, g and h in order of increasing distance from their parent star, have sizes similar to Earth.
The exoplanets are presumed to be tidally locked. The six closest to TRAPPIST-1 have been determined to be rocky, while the seventh, TRAPPIST-1h, requires additional observations to determine its characteristics due to its longer orbital period.
Mass estimates for the planets range from 0.41 Earth masses (M⊕) to 1.38 M⊕. Radii range from 0.76 Earth radii (R⊕) to 1.13 R⊕.
Spitzer, Hubble, and other telescopes will continue to make observations of the TRAPPIST-1 planetary system, but the best data will likely come from the James Webb Space Telescope (JWST), which is scheduled to launch in late 2018. JWST will allow the atmospheres and temperatures of many exoplanets to be characterized, which will help to settle whether the "habitable zones" of red dwarf stars are actually hospitable.
Here's a website dedicated to the star.
Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1 (DOI: 10.1038/nature21360) (DX)
Scientists have used the Spitzer Space Telescope to find a possible exoplanet or brown dwarf candidate, OGLE-2016-BLG-1190Lb, around 22,000 light years away near the center of the Milky Way galaxy. Spitzer is currently using transit photometry and gravitational microlensing to find exoplanets, a use the telescope wasn't originally designed for. Spitzer recently discovered five of the seven exoplanets around TRAPPIST-1 using the transit photometry method.
OGLE-2016-BLG-1190Lb is likely to be the first exoplanet Spitzer has found in the Milky Way's Galactic bulge using gravitational microlensing. At an estimated 13.4 ± 0.9 Jupiter masses, the object is right near the deuterium burning limit, the boundary dividing large gas giants from brown dwarfs.
The paper explains the significance of the discovery:
The discovery of Spitzer microlensing planet OGLE-2016-BLG-1190Lb is remarkable in five different respects. First, it is the first planet in the Spitzer Galactic-distribution sample that likely lies in the Galactic bulge, which would break the trend from the three previous members of this sample. Second, it is precisely measured to be right at the edge of the brown dwarf desert. Since the existence of the brown dwarf desert is the signature of different formation mechanisms for stars and planets, the extremely close proximity of OGLE-2016-BLG-1190Lb to this desert raises the question of whether it is truly a "planet" (by formation mechanism) and therefore reacts back upon its role tracing the Galactic distribution of planets, just mentioned above. Third, it is the first planet to enter the Spitzer "blind" sample whose existence was recognized prior to its choice as a Spitzer target. This seeming contradiction was clearly anticipated by Yee et al. (2015b) when they established their protocols for the Galactic distribution experiment. The discovery therefore tests the well-defined, but intricate procedures devised by Yee et al. (2015b) to deal with this possibility. Fourth, it is the first planet (and indeed the first microlensing event) for which the well-known microlens-parallax degeneracy has been broken by observations from two satellites. Finally, it is the first microlensing planet for which a complete orbital solution has been attempted. While this attempt is not completely successful in that a one-dimensional degeneracy remains, it is an important benchmark on the road to such solutions.
Scientists now have a good estimate for the age of one of the most intriguing planetary systems discovered to date– TRAPPIST-1, a system of seven Earth-size worlds orbiting an ultra-cool dwarf star about 40 light-years away. Researchers say in a new study that the TRAPPIST-1 star is quite old: between 5.4 and 9.8 billion years. This is up to twice as old as our own solar system, which formed some 4.5 billion years ago.
[...] At the time of its discovery, scientists believed the TRAPPIST-1 system had to be at least 500 million years old, since it takes stars of TRAPPIST-1's low mass (roughly 8 percent that of the Sun) roughly that long to contract to its minimum size, just a bit larger than the planet Jupiter. However, even this lower age limit was uncertain; in theory, the star could be almost as old as the universe itself. Are the orbits of this compact system of planets stable? Might life have enough time to evolve on any of these worlds?
Astrophysicists have modeled the effects of red dwarf star flare activity on the atmospheres of orbiting exoplanets, and found that heavy gases including oxygen would be lost quickly, even in the so-called "habitable zone":
[When] the scientists accounted for superflares, their new model indicates the violent storms of young red dwarfs generate enough high-energy radiation to enable the escape of even oxygen and nitrogen – building blocks for life's essential molecules.
"The more X-ray and extreme ultraviolet energy there is, the more electrons are generated and the stronger the ion escape effect becomes," Glocer said. "This effect is very sensitive to the amount of energy the star emits, which means it must play a strong role in determining what is and is not a habitable planet."
Considering oxygen escape alone, the model estimates a young red dwarf could render a close-in exoplanet uninhabitable within a few tens to a hundred million years. The loss of both atmospheric hydrogen and oxygen would reduce and eliminate the planet's water supply before life would have a chance to develop.
"The results of this work could have profound implications for the atmospheric chemistry of these worlds," said Shawn Domagal-Goldman, a Goddard space scientist not involved with the study. "The team's conclusions will impact our ongoing studies of missions that would search for signs of life in the chemical composition of those atmospheres."
The research has obvious implications for exoplanets like Proxima Centauri b.
YouTube video (20 seconds).
How Hospitable Are Space Weather Affected Habitable Zones? The Role of Ion Escape (DOI: 10.3847/2041-8213/836/1/L3) (DX)
Scientists using NASA's Kepler space telescope identified a regular pattern in the orbits of the planets in the TRAPPIST-1 system that confirmed suspected details about the orbit of its outermost and least understood planet, TRAPPIST-1h.
[...] Astronomers from the University of Washington have used data from the Kepler spacecraft to confirm that TRAPPIST-1h orbits its star every 19 days. At six million miles from its cool dwarf star, TRAPPIST-1h is located beyond the outer edge of the habitable zone, and is likely too cold for life as we know it. The amount of energy (per unit area) planet h receives from its star is comparable to what the dwarf planet Ceres, located in the asteroid belt between Mars and Jupiter, gets from our sun.
[...] The team calculated six possible resonant periods for planet h that would not disrupt the stability of the system, but only one was not ruled out by additional data. The other five possibilities could have been observed in the Spitzer and ground-based data collected by the TRAPPIST team.
[...] TRAPPIST-1's seven-planet chain of resonances established a record among known planetary systems, the previous holders being the systems Kepler-80 and Kepler-223, each with four resonant planets.
Previously: Three New Earth-Like Planets Discovered Around an Ultra Cool Red Dwarf
Seven Earth-Sized Exoplanets, Including Three Potentially Habitable, Identified Around TRAPPIST-1
Powerful Solar Flares Found at TRAPPIST-1 Could Dim Chances for Life
[A] team of European researchers has identified something else that could have an immense effect on habitability: the star's magnetic field. Under the right conditions, planets close to a star will experience a strong but variable magnetic field, which can cause induction heating. In the case of one system with several habitable zone planets, the induction heating could be strong enough to convert them into oceans of magma.
[...] The European team behind the new report focused on M dwarf stars. Because these are small, relatively cool objects, their habitable zones are close to the star and well within the region where the star's magnetic field is quite strong. They also have magnetic fields that are strong to begin with, sometimes in the area of thousands of Gauss. The magnetic field of our Sun is typically 10 to 1,000 times weaker.
Not all M dwarfs rotate quickly enough for this to matter. Proxima Centauri, which hosts the closest known exoplanet, takes more than 80 days to complete a rotation. But there is a nearby M dwarf that completes a rotation in only three days: TRAPPIST-1, which hosts at least seven planets, three of them in the habitable zone. So, the team decided to model how much of an effect induction heating might have on these bodies.
[...] For TRAPPIST-1c, the third planet out from the star, induction heating reaches more than 60 percent of the heat released in the planet by radioactive decay. That's enough to melt the entire surface, turning it into a magma ocean in nearly all the different model conditions sampled. The same conditions are likely on TRAPPIST-1d, the one in the habitable zone, where induction heating can be above half the amount of heat released by radioactive decay.
Red dwarf exolife killer or a way to expand the habitable zone further out?
Magma oceans and enhanced volcanism on TRAPPIST-1 planets due to induction heating (DOI: 10.1038/s41550-017-0284-0) (DX)
Previously: Seven Earth-Sized Exoplanets, Including Three Potentially Habitable, Identified Around TRAPPIST-1
Powerful Solar Flares Found at TRAPPIST-1 Could Dim Chances for Life
TRAPPIST-1h Orbital Details Confirmed
TRAPPIST-1 Older than Our Solar System
Hubble Observations Suggest TRAPPIST-1 Exoplanets Could Have Water
The red dwarf strikes again with 42 observed solar flares. Back in February, NASA and ESO announced the discovery of three potentially habitable Earth-like exoplanets in the TRAPPIST-1 system. Astronomers analyzing data from the Kepler space telescope have observed energetic solar flares which they believe could make it less likely that the TRAPPIST-1 system could host life.
Frequent flaring in the TRAPPIST-1 system - unsuited for life? (arXiv:1703.10130)
Related: Probability of CME Impact on Exoplanets Orbiting M Dwarfs and Solar-like Stars (DOI: 10.3847/0004-637X/826/2/195) (DX)