Posted on Jan 8, 2019
Our Sun is not one of the most abundant types of stars in our Milky Way. This award goes to red dwarfs, stars that are smaller and colder than our sun. In fact, red dwarves presumably contain most of the planet's population in our galaxy, reporting NASA's Hubble Site, which may be the number of tens of billions of worlds. Research by the NASA Kepler Space Telescope and other observatories has shown that rocky planets are common around these tiny stars. Some of these rocky worlds are orbiting within the habitable zones of several nearby red dwarfs. Temperate climates in such worlds can allow the oceans to exist on their surface, possibly feeding life.
That's the good news. The bad news is that many of these rocky planets can not harbor water and organic material, the necessary ingredients for life as we know it. The Earth, formed as a "dry" planet, was sown over hundreds of millions of years with icy material from comets and asteroids arriving from the outer solar system.
Red dwarfs, which are smaller and weaker than our Sun, are the most enduring stars in the galaxy. However, rocky planets orbiting red dwarfs may be boneless and lifeless, according to the new study. Water and organic compounds, essential to life as we know it, can be destroyed before they can reach the surface of young planets.
"The Earth, we know, has formed dry, with a hot, molten surface, and has accumulated atmospheric and other volatile water for hundreds of millions of years, being enriched by the frozen material of comets and asteroids transported from external solar system, "said co-investigator Glenn Schneider of the Steward Observatory in Tucson, Arizona.
This hypothesis is based on startling observations of a disk of dust and gas that erode rapidly surrounding the young red dwarf AU Microscopii (AU Mic) of Hubble and the Very Large Telescope of the European Southern Observatory (VLT) in Chile. Planets are born on disks like this.
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Drops of fast-moving material appear to be ejecting particles from the AU Mic disk. If the disc continues to dissipate at this fast rate, it will disappear in about 1.5 million years. In that short space of time, ice material from comets and asteroids could be removed from the disk. Comets and asteroids are important because they are believed to have rocky planets sown, such as Earth, with water and organic compounds, building blocks for life. If this same transport system is needed for planets in the AU Mic system, then they may end up "dry" and dusty – inhospitable to life as we know it.
The observations are conducted by John Wisniewski of the University of Oklahoma in Norman, whose team is composed of 14 astronomers from the US and Europe.
If the activity around the AU Mic is typical of the birthing process among red dwarfs, this could further reduce the prospects of habitable worlds throughout our galaxy. Earlier observations suggest that a torrent of ultraviolet light from young red dwarf stars quickly removes the atmosphere from any orbiting planet. This particular star is only 23 million years old.
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Research has shown that terrestrial planets are common around red dwarfs. In fact, they must contain most of the planet's population in our galaxy, which may be the number of tens of billions of worlds. The planets were found within the habitable zone of several nearby red dwarfs, but their physical characteristics are largely unknown.
Exploded by Blobs:
Observations by the Hubble Space Telescope Imaging Spectrograph (STIS) and the VLT show that the AU Mic circumflex disk is being excavated by bubbles of circumstellar material, which are acting as a snow blower, pushing small particles – possibly containing water and other volatiles. out of system. Researchers still do not know how bubbles were released. One theory is that powerful mass expulsions of the turbulent star drove them out. This energetic activity is common among young red dwarfs.
"These observations suggest that planets containing water may be rare around red dwarfs because all smaller bodies carrying water and organic products are blown out when the disk is excavated," explained Carol Grady of Eureka Scientific in Oakland , California. Hubble Observations.
Conventional theory holds that billions of years ago the Earth formed as a comparatively dry planet. Asteroids and gravitationally disturbed comets, rich in water from the cooler outer solar system, bombarded the Earth and sowed the surface with ice and organic compounds. "However, this process may not work in all planetary systems," Grady said.
The team determined the disk life span using an estimated disk mass from an independent study, as well as calculating the mass of the exhaust blobs in their STIS visible light data. The mass of each bubble is about four-tenths of a millionth of the Earth's mass. Disk mass – about 1.7 times more massive than Earth – is based on data from the Atacama Large Millimeter / submillimeter Array (ALMA).
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Although the mass of the rebellious drops seems small, the diameter of each drop could extend at least from the Sun to Jupiter. Currently, the team has detected six external bubbles, but it is possible that there is a continuous flow of them. Groups of bubbles that penetrate the disc can sweep the material quickly.
"The rapid dissipation of the disc is not something I would expect," Grady said. "Based on disk observations around more luminous stars, we expected disks around red dwarf stars to have a longer time. In this system, the disk will disappear before the star is 25 million years old. " She added that the AU Mic probably started with an outer edge of small icy bodies, such as the Kuiper belt found inside our own solar system. If the disk was not being eroded, it would have supplied ice to any dry internal planet.
Plumbing the mystery of the bubble
Hubble astronomers have discovered the bubbles in STIS's visible light images made in 2010-2011. As a continuation of the Hubble study, the SPHERE (High-Contrast Spectrum-Polarimetric Exoplanet Research) instrument mounted on the Very Large Telescope of the European Southern Observatory in Chile made near-infrared observations. Disk resources were suggested in observations made in 2004 by ground-based telescopes and Hubble's Advanced Camera for Surveys.
So far, the team has discovered blisters on the southeastern side of the disk, with ejection speeds estimated to be between 9,000 miles per hour and 27,000 miles per hour, fast enough to escape the star's gravitational claws. They currently range in distance from about 930 million miles to more than 5.5 billion miles from the star.
Hubble is also showing that these bubbles may not be just giant balls of dusty debris. The telescope resolved the substructure into one of the droplets, including a mushroom cover above the plane of the disk itself and a complex loop-like structure below the disk. "These structures can provide clues about the mechanisms that drive these bubbles," Schneider said.
"The AU microphone is ideally positioned," Schneider said. "But it's just one of about three or four red dwarf systems with known stellar scatter discs. The other known systems are usually about six times as far apart, so it is challenging to conduct a detailed study of the types of resources on these disks that we see in AU Mic. "
However, astronomers are beginning to identify some possibly similar activity in these other systems. "It shows that AU Mic is not unique," Grady said. "Actually, you could argue that being one of the closest systems of this type would be unlikely to be unique."
AU Mic observations show the importance of a star's disk environment in the formation and evolution of the planet. "What we've learned is that disks seem to be a normal part of the history of planetary systems," Grady said. "If you do not understand the disk of a star, you do not have a good understanding of the resulting planetary system."
The Daily Galaxy via Hubble site