Dawn (in orbit around Ceres) and the Mars rovers have been making all the news lately, but the plucky New Horizons probe has just crossed an astronomical milestone on her way to a close encounter with Pluto on July 14 of this year.
The erstwhile (dwarf) planet chaser is now less than one astronomical unit (AU) from its target. One AU is the average distance between the Sun and Earth, or about 93 million miles (149.6 million kilometers). http://pluto.jhuapl.edu/...
To put that in perspective:
New Horizons is now closer to Pluto than we are to the sun, but nearly 32.3 AU from the earth, or about 3 billion miles (4.8 billion Kilometers).
Mars and the rovers are about as far from earth as they ever get, about 200 million miles (320 million kilometers).
New Ceres satellite Dawn is out there in the space between Mars and Jupiter, but still only about 305 million miles (488 million kilometers) from earth.
In fact, only 4 human-made objects, launched by NASA between 1972 and 1977, have traveled further earth than New Horizons. Pioneer 10 (112AU), Pioneer 11 (91AU), and Voyager 2 (107AU), are the most distant human probes in the solar system. Voyager 1, more than 130 AU away, marks humanity's first venture into interstellar space.
When New Horizons makes its close pass of Pluto, she will be the first probe to reach a Kuiper Belt object and will execute the most distant rendezvous with any celestial object to date. If all goes well, she will break her own record by visiting a second, more distant, object after the Pluto encounter.
Much of the probe's activity is now geared toward setting up for the final approach, but, starting in May, New Horizons will be able to capture Pluto images that exceed the quality of those taken by the Hubble Space Telescope. When all is said and done, we will know more about the composition of Pluto, its atmosphere, and its moons than ever before.
