Young Planets Orbiting Red Dwarfs May Lack Ingredients for Life

[HubbleSite]

Our Sun is not one of the most abundant types of star in our Milky Way galaxy. That award goes to red dwarfs, stars that are smaller and cooler than our Sun. In fact, red dwarfs presumably contain the bulk of our galaxy's planet population, which could number tens of billions of worlds. Surveys by NASA's Kepler Space Telescope and other observatories have shown that rocky planets are common around these diminutive stars. Some of these rocky worlds are orbiting within the habitable zones of several nearby red dwarfs. The temperate climates on such worlds could allow for oceans to exist on their surface, possibly nurturing life.

That's the good news. The bad news is that many of these rocky planets may not harbor water and organic material, the necessary ingredients for life as we know it. Earth, which formed as a "dry" planet, was seeded over hundreds of millions of years with icy material from comets and asteroids arriving from the outer solar system.

If the same life-nurturing process is needed for planets around red dwarfs, then they may be in trouble. Researchers using the Hubble Space Telescope and the European Southern Observatory’s Very Large Telescope (VLT) in Chile have discovered a rapidly eroding dust-and-gas disk encircling the young, nearby red dwarf star AU Microscopii (AU Mic). The disk is being excavated by fast-moving blobs of material, which are acting like a snowplow by pushing small particles — possibly containing water and other volatiles — out of the system. Astronomers don’t yet know how the blobs were launched. One theory is that powerful mass ejections from the turbulent star expelled them. Such energetic activity is common among young red dwarfs.

If the disk around AU Mic continues to dissipate at the current pace, it will be gone in about 1.5 million years, which is the blink of an eye in cosmic time. Smaller bodies, such as comets and asteroids, could be cleared out of the disk within that short time span. Planets, however, would be too massive to be displaced. Without enrichment from comet and asteroid material, the planets may end up dry, dusty, and lifeless.

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