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People Behind the Science

Gerard Peter Kuiper (1905–1973)

erard Kuiper was a Dutch-born U.S. formation of protoplanets still appears to
Gastronomer best known for his stud- be unworkable, partly because it involves
ies of lunar and planetary surface features the condensation of only 1.5 percent of the
and his theoretical work on the origin of the original interstellar gas cloud, thus leaving
planets in the solar system. the rest of the material unaccounted for.
Kuiper was born on December 7, 1905, Kuiper’s work on planetary features
at Harenkarspel, the Netherlands. After proved to be far more fruitful. In 1948 he
completing his education in his own coun- predicted that carbon dioxide was one
try, he immigrated to the United States in of the chief constituents of the Martian
1933 and four years later became a natural- atmosphere—a theory he was able to see
ized U.S. citizen. He joined the staff of the confirmed when the era of research into that
Yerkes Observatory, which is affiliated with planet began in 1965 with the Mariner 1 and
the University of Chicago. Between 1947 Mariner 2 space probes to Mars. He also
and 1949 he was director of the observa- discovered the fifth moon of Uranus in
tory, returning for a second term in this of- 1948, which he called Miranda; and in 1949
fice from 1957 to 1960. From 1960 until his he discovered the second moon of Nep-
death he held a similar position at the Lunar tune, Nereid. Compared with Neptune’s
and Planetary Laboratory at the University first moon, Triton, which has a diameter
of Arizona, and he was closely linked with of 3,000 km (1,864 mi), Nereid is a dwarf
the U.S. space program. He died in Mexico and has an eccentric orbit; its distance
City on December 24, 1973. from Neptune varies by several million
Kuiper’s work on the origin of the plan- products. In fact, it was found that this con- kilometers. Kuiper’s spectroscopic studies
ets stemmed from the theoretical discrepan- densation theory was inadequate to account of the planets Uranus and Neptune led to

cies that arose from new twentieth- century for the temperature or the amount of mate- the discovery of features, subsequently
hypotheses on galactic evolution. One of rial that makes up the bulk of the planets named Kuiper bands, found at wavelengths
the more favored of these theories is that in the solar system. To compensate for this, of 7,500 angstroms (Å) (7.5 × 10−7 m),
stars, and presumably planets, are formed Kuiper and his colleagues proposed that the which have been identified as being due to
from the condensation products of inter- mass of the cloud from which the planets the presence of methane.
stellar gas clouds. For this condensation to were formed was much greater than the During his working life, Kuiper insti-
take place, the gravitational effects pulling present mass of the planets, and suggested gated many planetary research programs,
the cloud together must exceed the expan- that the mass of the original interstellar and he played a vital role in the U.S. space
sive effect of the gas pressure of the cloud. gas cloud was approximately one-tenth the probe program during the late 1960s and
However, calculations of this hypothetical mass of the Sun, or 70 times the total mass early 1970s. In recognition of his work,
process showed that under given condi- of the planets. The results of condensation the International Astronomical Union has
tions of temperature and density, there was according to these new conditions would named a ray crater on the planet Mercury
a lower limit to the size of the condensation produce “protoplanets.” But the idea of the after him.

Source: From the Hutchinson Dictionary of Scientific Biography, © Research Machines, 2008, all rights reserved. Helicon Publishing is a division of Research Machines, as published under
license in AccessScience.

2
3
planet is in the orbit, since the distance from the focus to a given semimajor axis, or t ∝ d . When the time is expressed in Earth
position varies around the ellipse. The point at which an orbit units of one year for a revolution and a radius of astronomical
comes closest to the Sun is called the perihelion, and the point unit, the distance to a planet can be determined by observing
at which an orbit is farthest from the Sun is called the aphelion. the period of revolution and comparing the orbit of the planet
The shortest line from a planet to the Sun at perihelion means with that of Earth. For example, suppose a planet is observed to
that the planet moves most rapidly when here. The short line require 8 Earth years to complete one orbit. Then
and rapidly moving planet would sweep out a certain area in a 2 3
d(planet)
t(planet)
certain time period, for example, one day. The longest line from _ _
=

a planet to the Sun at aphelion means that the planet moves t(Earth) 2 d(Earth) 3
2
most slowly at aphelion. The long line and slowly moving planet _ _ 3
(8)
(distance)

would sweep out the same area in one day as was swept out 1 = 1
at perihelion. Earth travels fastest in its orbit at perihelion on 3
64 = (distance)
about January 3 and slowest at aphelion on about July 1. 3

U
64 A

Kepler’s third law states that the square of the period distance = √
of a planet’s orbit is proportional to the cube of that planet’s distance = 4 AU
398 CHAPTER 15 The Solar System 15-22