Q: What do the European Space Agency’s Mars Express, India’s Mars Orbiter Mission and 16 of NASA’s spacecraft, scientific instruments and rovers all have in common?
A: They’ll put in overtime hours this week observing comet C/2013 A1 as it sweeps past Mars.
C/2013 A1 (also known as Siding Spring, after the Australian observatory where it was discovered last year) weighs as much as a small mountain, is travelling 126,000 mph, and, on Sunday will pass within a mere 87,000 miles of the Red Planet—which, astronomically speaking, is a near-miss. That’s less than half the distance between the moon and Earth.
This is the first time Siding Spring has ventured into the inner solar system. The comet originated in the Oort Cloud, a donut-shaped region far beyond Pluto’s orbit that contains trillions of icy bodies. By analyzing the comet’s makeup, scientists hope to learn more about conditions in the solar system’s early history.
The array of instruments poised to study Siding Spring will focus on the comet’s size, composition, and rotational speed. NASA’s MAVEN (Mars Atmosphere and Volatile EvolutioN) orbiter, which only recently arrived at Mars, will examine the effect the close encounter has on the planet’s atmosphere. There is a chance that material given off by the comet could cause brilliant Martian auroras.
Although the risk is small, there is also a chance that some instruments in Mars orbit could be harmed by dust from the comet. As a precautionary measure, NASA is positioning its Mars orbiters behind the planet at the time of close approach to ensure their safety.
Even though Siding Spring boasts a nucleus 700 meters across and has a tail 621,000 miles long, it won’t come close enough to Earth for us to see it with the naked eye. Amateur and professional astronomers in the southern hemisphere will be watching with telescopes, however.