December 7 – Happy Birthday, Gerard Peter Kuiper

Gerard Peter Kuiper is considered an American astronomer, even though he was born in the Netherlands (on this day in 1905).

Kuiper was brought up in north Holland and went to university there as well, but as soon as he got his doctorate, he moved to the United States, where he lived and worked for the rest of his life. He became a U.S. citizen in 1937.

Kuiper made a number of interesting discoveries. He was the first to spot Uranus’s moon Miranda and Neptune’s moon Nereid, and he was first to discover a moon in the solar system with an atmosphere (Saturn’s moon Titan).

Miranda

Nereid

Titan’s atmosphere!

Kuiper is best remembered, however, for his suggestion that there was once a belt of small bodies beyond Neptune’s orbit, leftovers from the formation of the solar system. Kuiper assumed that the huge gas giants would have gravitationally swept space clean of such objects by now—but there actually still are thousands and thousands of orbiting bodies beyond the planets. Every once in a while, something “jiggles” one of them, and it shoots toward the sun, becoming what we call a comet.

We now call that region of the solar system (the region beyond Neptune’s orbit to about 55 Astronomical Units) the Kuiper belt. The Kuiper belt is similar to the asteroid belt that lies between the orbits of Jupiter and Mars. However, the Kuiper belt region is way huger, and the orbiting objects are made mostly of frozen ices rather than rock and metal.

Several of the bodies in the Kuiper belt are large enough to be classified as dwarf planets, including Pluto, Haumea, and Makemake. All the dwarf planets in this category are called “plutoids” in Pluto’s honor—probably a consolation prize for Pluto being bumped out of the “planet” category!

Match each planet below with the objects that are orbiting around it:

Read about comets here.

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