Before entering into orbit around Comet 67P Churyumov-Gerasimenko on August 6, the European Space Agency’s (ESA) Rosetta probe took its target’s temperature, revealing it to be warmer than scientists thought.
Between July 21 and 31, Rosetta traveled from 8,699 miles away from the comet to 3,106 miles (14,000 to 5,000 kilometers). As it headed toward its destination, the probe imaged the comet, showing some sections of its surface to be more elevated than others along with a cratered landscape. These markings were visible from a distance of 145 miles (234 km).
The probe took the comet’s temperature using VIRTIS, a spectrometer that takes images thermally, in visible light, and in the infrared.
As of mid-July, VIRTIS measured Comet 67P’s surface temperature at minus 94 degrees Fahrenheit (minus 70 degrees Celsius). That unexpected high temperature took astronomers by surprise because comets covered in ice, like this one, usually are much colder. The warmer temperature might indicate the comet has a dusty surface with only some patches of ice. Similar surfaces have been found on other comets, such as 1P/Halley, ESA representatives noted.
In Earth-based observations, 67P has been found to have a low reflectivity, which is consistent with a surface that is more dusty than icy.
Rosetta will orbit 67P as it heads toward its perihelion between the orbits of Mars and Earth. At that point, it will release a lander named Philae onto the comet’s surface. VIRTIS will take the temperatures of various regions on the surface of 67P between now and November, when the lander is deployed. It will also assist scientists in choosing a landing site by returning data about the surface, including its density and permeability as well as the way it conducts heat.
The spectrometer will measure and analyze temperature changes in various regions of the comet’s surface, helping scientists understand the changes a comet undergoes as it heads toward the sun.