Comet 3I/ATLAS, the interstellar interloper currently zipping through our solar system, cannot easily be observed from Earth right now, because it is on the other side of the solar system. The sun is not directly blocking the view, but trying to make out a dim comet within the daytime glare is nigh impossible.
But Mars is also on that side of the solar system right now, and spacecraft there have been able to photograph the comet, which is just the third object known to have come from elsewhere in the Milky Way galaxy.
On Tuesday, the European Space Agency released a short movie of images that one of its spacecraft, the ExoMars Trace Gas Orbiter, took on Saturday as the comet made its closest approach to Mars.
The images successfully captured a bright dot of the comet moving among the more distant stars, an impressive achievement for a camera that “is designed to observe Mars,” said Nicolas Thomas, a professor of experimental physics at the University of Bern in Switzerland and the principal investigator for the instrument.
Typically, the orbiter, which has studied Mars since 2016, points its camera downward at the surface 250 miles below, snapping about three pictures a second with an exposure time of about 1.5 milliseconds, Thomas said. Here, it was aimed at a dot nearly 20 million miles away, with five-second exposures, trying to make out something that was between 1/10,000th and 1/100,000th as bright as its usual observations.
Five seconds was long enough to gather enough light, but not too long for the dot to become smeared too much by the motion of the comet.
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