Ecology
Last July, NASA's Solar Dynamics Observatory satellite witnessed what happened to comet SOHO (C/2011 N3), which passed only 100,000 kilometers above the Sun's photosphere. The poor comet left the Sun with nothing but a wet spot.
Five months later, in December of that year, another comet called Lovejoy (C/2011 W3) also found itself in the Sun's “death zone”, about 14,000 kilometers from the photosphere, but it succeeded survive even though it has lost most of its mass.
So why did Comet Lovejoy survive and SOHO die? Astronomers have been struggling with this mystery since the 1980s, and today they seem to have found the answer to why some comets survive the sun's blazing rays while others don't.
One of the study's authors, John Brown, the Royal Astronomer of Scotland, explained that the secret lies in the mass and orbital trajectory of comets.
Most of the dust ice balls we call comets date back to the formation of the solar system and orbit within the Oort Cloud. Sometimes comet orbits are disturbed and they head towards the Sun.
As soon as a comet appears within the solar system, the ice begins to melt, and the comet develops a long tail due to the solar wind. How much material a comet sheds depends on its size. For example, Comet Hale-Bopp was very massive and weighed tens of millions of tons, so it managed to cross the danger zone near the Sun and stay alive.
Smaller comets, which are more common, weigh about 1,000 tons. The material of these objects evaporates usually due to solar heat and friction with atmospheric gas.
According to Brown's analysis, comets lose their mass in several ways. So-called “solar divers” have an orbit in the lower part of the atmosphere, about 7,000 kilometers under the photosphere.
In this case, sunlight does not affect the comet; it loses mass due to the resistance of the solar gas that surrounds it. This usually happens fairly quickly and comets collapse when they collide with the denser layers of the lower solar atmosphere. Such comet explosions can be traced, as they look very much like prominences.
Comets SOHO and Lovejoy are such “solar divers”. These comets lose mass due to sunlight and atmospheric resistance and emit weaker ultraviolet radiation, but they can still be detected.
Why was SOHO destroyed? The thing is that Comet Lovejoy had a large mass, that is, its material did not have time to completely evaporate. For now, this remains a hypothesis, so scientists will continue to observe comets orbiting near the Sun to confirm their assumptions.