Culver: Passing craft could give insight on Pluto

Roger B. Culver

In a little over a week, for the third time in less than a year, a spacecraft will examine a heretofore unexplored object in the solar system. Last November, the Rosetta space probe was placed into orbit about the nucleus of Comet 67 P and soft landed an instrument package on its surface. Earlier this year, the Dawn space craft went into orbit about the dwarf planet Ceres in the asteroid belt between the orbits of Mars and Jupiter. Eight days from now, a third space craft, New Horizons, will fly past another, far more controversial dwarf planet, Pluto.

Pluto was discovered in 1930 at the Lowell Observatory in Flagstaff, Arizona by a young and enthusiastic astronomer named Clyde Tombaugh. It was a great story. The name of the newly discovered planet, Pluto, was suggested by a young girl from England and its first two letters were the initials of Percival Lowell who had founded Lowell Observatory in 1894 and had been the driving force behind the decades-long search for what he called the “transneptunian planet”. With the discovery, Walt Disney in 1931 changed the name of his early cartoon canine Rover to Pluto, who then became the iconic and lovable Disney character we know today, thus cementing pooch and planet over the decades since.

Unfortunately, the fairy tale did not last. Shortly after Pluto’s discovery, the shape and orientation of Pluto’s orbital path were found to more closely resemble those of an asteroid rather than a planet. In subsequent years, additional astronomical observations and discoveries found that Pluto is an object that is roughly 1/8 the size of the earth and about 1/50 of the earth’s mass. Moreover, during the past 20 years, astronomers have discovered nearly 1,000 “dusty snow-balls” orbiting about the sun beyond Neptune in a region of the solar system called the Kuiper belt. One of these Kuiper belt objects, called Eris, was found to be of comparable size to Pluto, and it was this discovery that dealt the death blow to Pluto’s planetary status.

In 2006 the International Astronomical Union made the controversial decision to demote Pluto to the status of a “dwarf” planet, thereby placing it in the same class as Eris and Ceres but also serving to ignite a debate over Pluto’s status that simmers to this day. Despite its small size, orbital characteristics and location in one of the debris fields of the solar system, Pluto nonetheless is now known to have five satellites – thus surpassing the total number of satellites in orbit about the planets Mercury, Venus, Earth and Mars combined. In addition, Pluto also possesses a thin atmosphere, while Mercury has none. So the debate rages on.

As New Horizons flashes by Pluto in upcoming days, its package of sophisticated instruments hopefully will provide astronomers with a great deal more insight concerning this remote world. For now, however, Pluto’s dwarf planet status is the official astronomical position, but one just knows that somehow the curmudgeonly spirits of Clyde Tombaugh and Percival Lowell will not let this stand as the last word on the status of Pluto. Perhaps New Horizons will be the vehicle by which the controversial 2006 IAU decision might be overturned.

Elsewhere in the sky: After a splendid conjunction a few days ago, the planets Venus and Jupiter will still form an attractive pair in the early evening western sky all month long as they sink ever closer to the oncoming solar twilight. At present, this planetary duo can be seen for about two hours after sunset, but by month’s end, these objects will be setting less than 45 minutes after the sun.

The planet Saturn is visible to the south at the onset of darkness and glows as a golden hued object above and to the right of the “T” of the constellation of Scorpius. Compare and contrast Saturn’s color with that of the nearby first magnitude Scorpius star Antares.

The planets Mercury and Mars are too close to the sun to be easily seen in July.

Roger Culver is an astronomer who teaches at CSU.