On November 4, 2010, NASA's EPOXI spacecraft went within 450 miles of Comet Hartley 2. Designated officially as 103P/Hartley 2, the comet thus became the fifth comet with close-up images.
Hartley 2 is a short period comet that about six and a half years to orbit the Sun and is also a small comet with about 1.5 km in diameter.
But the Solar and Heliospheric Observer (SOHO), better known for its observations of the sun, also observed comet Hartley 2. Together, the two returned data about what appears to be an irregular comet, ejecting chunks of ice and losing water at a very fast pace.
These findings were described in an article of the June 10, 2011 issue of the Astrophysical Journal Letters.