The search for life beyond Earth is entering a new era. Only 15% of the Milky Way’s stars are sun-like. Nearly half of these stars have binary companions, which suppress the formation of planets. A small fraction of the results in nature can be found by searching for Earth analogs around single solar-type stars.
Searching for Planetary Systems Other Than Our Solar System
“How frequently is life found elsewhere?” asked the Research teams at the University of Cambridge and the University of Liège in Belgium. This simple change in words implies that we should also investigate planetary systems not related to the solar system. It would be disappointing and even surprising if Earth were all that was needed to ensure habitability throughout the Universe.
It is encouraging that the planets have so much in common with Earth, which bodes well for the search to find life elsewhere.
“No matter what we find by studying planets orbiting ultra-cool dwarfs, we cannot lose. We can only learn,” said the researchers. “If we manage to identify the presence of life on a planet similar to those in the TRAPPIST-1 system, then we can start measuring how frequently biology emerges in the universe. We could have the first clues of extraterrestrial biology in a decade!”
The team was formed in March 2017. reportedTRAPPIST-1 is a nearby star that is orbited around seven planets with similar mass and size to Earth. TRAPPIST-1 stars is a red M dwarf that can barely fuse hydrogen. It has 9% mass, 12% radius, and 0.06% as much luminosity than our yellow Sun. The seven planets orbit TRAPPIST-1 with very short periods, ranging from 1.5 – 18.8 days. TRAPPIST-1’s temperature is extremely low, making it difficult for the planets to sustain liquid water. Three of these planets are particularly likely to be habitable as they receive approximately the same amount from their star’s energy as the Earth from the Sun.
“That the planets are so similar to Earth bodes well for the search for life elsewhere,” University of Birmingham astronomer Amaury Triaud.
Targeting ultra-cool Dwarf Systems
Ultra-cool dwarfs will become an obvious target once we have reset the goal to measure biology’s total frequency. Half the stars in the Milky Way have masses less than one-quarter of the Sun’s. Preliminary results show that rocky worlds orbit low-mass stars, including super-cool dwarf systems. This could be more than if they orbit Sun-like stars. The discovery and study of Earth-like, temperate planets is also easier with ultra-cool dwarfs.
These stellar properties are what make ultra-cool dwarfs so scientifically beneficial. They also influence how exoplanets are identified and how we plan to study their atmospheres. Transits are events that occur when planets pass in front of their star. These transits are how the TRAPPIST-1 ones were discovered. A planet’s transit creates a shadow that tells us the depth of the star’s surface. The darker the shadow, and the larger the planet is, the more it hides. Ultra-cool dwarfs are small and the transit of an Earth-sized Earth-sized planet before TRAPPIST-1 is about 80 times more prominent than a similar transit against a larger, Sun-like star.
Is there Life in the TRAPPIST-1 Star System – “Twice as Old as Our Solar System”
During a transit, any gasses in the planet’s atmosphere change the appearance of starlight streaming through. The atmospheric signature of ultra-cool dwarfs increases by around a factor of 80. The atmospheres of TRAPPIST-1 planets can be detected using existing and future facilities such as the James Webb Space Telescope. This is in contrast to the many decades of technological advancement required to study an analog Earth’s atmosphere.
The Reliable Atmospheric Signal
It takes many transits to extract an atmospheric signal. TRAPPIST-1 is a great system for this purpose. Transits of temperate planets around tiny, ultra-cool dwarfs occur once per week for planets exactly like Earth, and once a year for planets with similar characteristics.
Signs of biologically-produced gases
According to the authors, scientists have been studying the compositions and molecules of giant planets surrounding other stars since the beginning. The TRAPPIST-1 system has allowed us to expand our explorations to larger planets. They will first try to identify the greenhouse gas content in the atmosphere and determine if the surface conditions are suitable for liquid water. Then we will seek out signs of biologically produced gasses, analogous to ways that living organisms have transformed the composition of Earth’s atmosphere.
These super-cool dwarf stars could be found in many other systems around the galaxy.
It will be difficult to claim a discovery of life. It is not possible to rely on the detection one gas. Instead, we will need to detect multiple gases and measure their relative abundances. False positives will be a major concern. Repeated stellar flares, for example, could increase oxygen levels in the atmosphere without any life.
Fake Positives
Because we can compare the planets of the TRAPPIST-1-system, it is a significant asset. They all share the same nebular Chemistry and have a similar history of meteoritic impact and flares. It will be easier to identify false positives here than in systems that contain only one or two planets with similar climates, which could make them Earth-like.
TRAPPIST-1 isn’t a singular discovery. These ultra-cool dwarf stars could also be found in other systems around the galaxy. They used the TRAPPIST (Transiting Planets & Planetesimals Small Telescopes), facility to locate the TRAPPIST-1 moons. This was only the prototype for a larger planet survey. SPECULOOS (Search for habitable planets that eclipse ultra-cool stars)
According to the team, we expect to find more Earth-sized, rock planets around dwarf star. They will use this sample to explore the different climates of these worlds. The solar system has two planets: Venus, and Earth. We will discover many types of environments.
SPECULOOS will be used by the team to address many objections scientists have raised regarding the habitability planets surrounding ultra-cool dwarfs. One argument is the fact that such planets are tidally-locked, meaning they have permanent day/night sides. Planets orbiting in close proximity around small stars could excite each other’s orbits, leading to major instabilities. Ultra-cool dwarf stars frequently flare up, emitting ultraviolet and X-rays that might vaporize a planet’s oceans into space.
TRAPPIST-1 is certain to remain the most important JWST target for studying potentially habitable Earth size planets.
The Last Word –“TRAPPIST-1 is the Ultimate James Webb Space Telescope Target”
Send an email to The Daly Galaxy co-author, Astronomer Michael GillonAt University of Liège wrote: “TRAPPIST-1 remains the only known planetary system around an ultracool dwarf star (UCDS). TESS has discovered a few rocky planet systems around M-dwarfs of very low mass, but they are still too large and hot to be included in the UCDS category. This was to be expected: TESS’ telescopes are too small to efficiently explore nearby UCDS for rocky planets. Our ground-based transit search system SPECULOOS has been operating since 2019. It is aiming to accomplish such exploration. It just made its first discovery: a system that contained at least 2 planets slightly larger then Earth, around an UCD slightly bigger than TRAPPIST-1 (Delrez and al., in prep.). One of these planets lies in the star’s habitable zone. However, TRAPPIST-1’s detailed characterization makes it much more intriguing. This is for the reasons that this article explains. PaperTRAPPIST-1 is certain to remain THE ultimate JWST goal for the study of potentially habitable Earth size planets.
“We are of course thrilled by the successful launch of JWST!,” Gillon continued in his email. “The deployment of the telescope has also started with success, while it is still on its way to its final orbit. It should be operational by April or May. About 200 hours have been spent with the telescope on TRAPPIST-1, the first JWST Cycle (up until mid-2023). In the second half of 2022, we should have the first data ready for analysis. We look forward to analysing them and using them for searching for atmospheric traces around the seven planets.
“We still consider it possible to discover chemical traces of biological activity on some TRAPPIST-1 planets with JWST,” Gillon concludes. “But one step at a time. First we have to determine if these worlds have maintained a significant atmosphere. This information should be available within the first 2 years of JWST before 2024. We will intensify our observation of TRAPPIST-1 using JWST to identify the chemical compositions and possible detect a strong chemical disequilibrium indicating biological origin. We’ll see! In any case, the next few years are going to be extremely exciting!”
“Rocky planets transiting ultra cool dwarfs are our fastest route towards exploring and understanding alien climates, and initiate the search for evidence of biological activity beyond the Solar system,” Amaury Triaud told The Daily Galaxy. “They might also represent the largest population of rocky planets in the Universe. The TRAPPIST-1 was the first, and it is the only such super-cool dwarf system that can be viewed by the Webb telescope. However many others are suspected and our six SPECULOOS telescopes are hard at work to discover new transiting ultra-cool dwarf systems to turn the Webb to.”
Image credit top of page: Artist’s view at top of page of planets transiting a red dwarf star in the TRAPPIST-1 system. Credit: NASA, ESA and STScI
Maxwell Moe, astrophysicist, NASA Einstein Fellow University of Arizona via Michael Gillon, Amaury Triaud University of Cambridge
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Maxwell Moe (astrophysicist, NASA Einstein Fellow University of Arizona), Maxwell Moe Max can usually be found at Kitt Peak National Observatory on two nights per week exploring the mysteries and wonders of the Universe. Max earned his Ph.D. in Astronomy in 2015 from Harvard University.
