discoveries.
Any astronomer’s choice of the four most interesting problems will be idiosyncratic and I know many would make choices different from mine. Among other candidate mysteries are what 90 percent of the Universe is made of (we still don’t know); identification of the nearest black hole; the bizarre putative result that the distances of galaxies are quantized—that is, galaxies are at certain distances and their multiples but not at intermediary distances; the nature of gamma ray bursters, in which the equivalent of whole solar systems episodically blow up; the apparent paradox that the age of the Universe may be less than the age of the oldest stars in it (probably resolved by the recent conclusion, using Hubble Space Telescope data, that the Universe is 15 billion years old); the investigation in Earth laboratoriesof returned cometary samples; the search for interstellar amino acids; and the nature of the earliest galaxies.
Unless there are major cuts in the funding for astronomy and space exploration worldwide—a doleful possibility by no means unthinkable—here are four questions * of enormous promise:
1. Was There Ever Life on Mars? The planet Mars is today a bone-dry frozen desert. But all over the planet there are clearly preserved ancient river valleys. There are also signs of ancient lakes and perhaps even oceans. From how cratered the terrain is, we can make a rough estimate of when Mars was warmer and wetter. (The method has been calibrated by cratering on our Moon and radioactive dating from the half-lives of elements in lunar samples returned by
Apollo
astronauts.) The answer is about 4 billion years ago. But 4 billion years ago is just the epoch in which life was arising on Earth. Is it possible that there were two nearby planets with very similar environments, and life arose on one but not the other? Or did life arise on early Mars, only to be wiped out when the climate mysteriously changed? Or might there be oases or refuges, perhaps subsurface, where some forms of life linger into our own time? Mars thus raises two fundamental enigmas for us—the possible existence of past or present life, and the reason that an Earth-like planet has become locked into a permanent ice age. This latter question may be of practical interest to us, a species that is busily pushing and pulling on its own environment with a very poor understanding of the consequences.
When
Viking
landed on Mars in 1976, it sniffed the atmosphere, finding many of the same gases as in the Earth’s atmosphere—carbon dioxide, for example—and a paucity of gases prevalent in the Earth’s atmosphere—ozone, for example.What’s more, the particular variety of molecule, its isotopic composition, was determined and was in many cases different from the isotopic composition of the comparable molecules on Earth. We had discovered the characteristic signature of the Martian atmosphere.
A curious fact then transpired. Meteorites—rocks from space—had been found in the Antarctic ice sheet, sitting directly on top of the frozen snows. Some had been discovered by the time of
Viking
, some after; all had fallen to Earth before the
Viking
mission, often tens of thousands of years before. On the clean Antarctic ice shelf, they were not difficult to discern. Most of the meteorites so collected were brought to what in the
Apollo
days had been the Lunar Receiving Laboratory in Houston.
But funding is very meager at NASA these days, and not even a preliminary look at all these meteorites had been performed for years. Some turned out to be from the Moon—a meteorite or comet impacting the Moon, spraying Moon rocks out into space, one or some of which land in Antarctica. One or two of these meteorites come from Venus. And astonishingly, some of them, judging by the Martian atmospheric signature hidden away in their minerals—come from Mars.
In 1995—96, scientists at NASA’s Johnson Space Flight Center finally got around to examining one
Any astronomer’s choice of the four most interesting problems will be idiosyncratic and I know many would make choices different from mine. Among other candidate mysteries are what 90 percent of the Universe is made of (we still don’t know); identification of the nearest black hole; the bizarre putative result that the distances of galaxies are quantized—that is, galaxies are at certain distances and their multiples but not at intermediary distances; the nature of gamma ray bursters, in which the equivalent of whole solar systems episodically blow up; the apparent paradox that the age of the Universe may be less than the age of the oldest stars in it (probably resolved by the recent conclusion, using Hubble Space Telescope data, that the Universe is 15 billion years old); the investigation in Earth laboratoriesof returned cometary samples; the search for interstellar amino acids; and the nature of the earliest galaxies.
Unless there are major cuts in the funding for astronomy and space exploration worldwide—a doleful possibility by no means unthinkable—here are four questions * of enormous promise:
1. Was There Ever Life on Mars? The planet Mars is today a bone-dry frozen desert. But all over the planet there are clearly preserved ancient river valleys. There are also signs of ancient lakes and perhaps even oceans. From how cratered the terrain is, we can make a rough estimate of when Mars was warmer and wetter. (The method has been calibrated by cratering on our Moon and radioactive dating from the half-lives of elements in lunar samples returned by
Apollo
astronauts.) The answer is about 4 billion years ago. But 4 billion years ago is just the epoch in which life was arising on Earth. Is it possible that there were two nearby planets with very similar environments, and life arose on one but not the other? Or did life arise on early Mars, only to be wiped out when the climate mysteriously changed? Or might there be oases or refuges, perhaps subsurface, where some forms of life linger into our own time? Mars thus raises two fundamental enigmas for us—the possible existence of past or present life, and the reason that an Earth-like planet has become locked into a permanent ice age. This latter question may be of practical interest to us, a species that is busily pushing and pulling on its own environment with a very poor understanding of the consequences.
When
Viking
landed on Mars in 1976, it sniffed the atmosphere, finding many of the same gases as in the Earth’s atmosphere—carbon dioxide, for example—and a paucity of gases prevalent in the Earth’s atmosphere—ozone, for example.What’s more, the particular variety of molecule, its isotopic composition, was determined and was in many cases different from the isotopic composition of the comparable molecules on Earth. We had discovered the characteristic signature of the Martian atmosphere.
A curious fact then transpired. Meteorites—rocks from space—had been found in the Antarctic ice sheet, sitting directly on top of the frozen snows. Some had been discovered by the time of
Viking
, some after; all had fallen to Earth before the
Viking
mission, often tens of thousands of years before. On the clean Antarctic ice shelf, they were not difficult to discern. Most of the meteorites so collected were brought to what in the
Apollo
days had been the Lunar Receiving Laboratory in Houston.
But funding is very meager at NASA these days, and not even a preliminary look at all these meteorites had been performed for years. Some turned out to be from the Moon—a meteorite or comet impacting the Moon, spraying Moon rocks out into space, one or some of which land in Antarctica. One or two of these meteorites come from Venus. And astonishingly, some of them, judging by the Martian atmospheric signature hidden away in their minerals—come from Mars.
In 1995—96, scientists at NASA’s Johnson Space Flight Center finally got around to examining one
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