Magazine article Science News

The Solar System's Big Bang: Finding Signs of a Lost Beginning

Magazine article Science News

The Solar System's Big Bang: Finding Signs of a Lost Beginning

Article excerpt

Gone. Vanished. Lost.

When it comes to the early history of the solar system, planetary scientists must contend with a case of nearly system-wide amnesia.

Although the solar system formed nearly 4.6 billion years ago, researchers have a pretty good record that goes back only 3.9 billion years. Yet those first 700 million years proved critical to all that followed. That's when the planets coalesced and water and other compounds essential to life were delivered to the inner planets.

What's more, according to a leading theory now being explored in detail, that early era was capped by a truly cataclysmic event. About 3.9 billion years ago, the movement of the most massive planets dramatically rearranged the outer solar system. The shifting planets freed rocky and icy bodies from the solar system's edge, commencing a bombardment of the entire retinue of planets.

Filling in the details of this violent era in the solar system's development has met serious obstacles. On Earth and many of the other planets, billions of years of volcanic eruptions, quakes, erosion and burials have all but erased solid evidence of the solar system's earliest chapters. But Earth's crater-scarred moon, quiescent and lacking an atmosphere that could destroy incoming space debris, appears to be a rare and nearby exception.

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Now new observations and reanalyses of old moon data, along with progress from theorists, have renewed interest in reconstructing the events of the solar system's preadolescence.

"If we don't understand the [earliest] years of the solar system, then we don't really understand how the planets formed, and where we came from," says Bill Hartmann of the Planetary Science Institute in Tucson. "And that applies to both biology and how planetary systems look, and what fraction of the planets [beyond the solar system] might be habitable."

Planetary scientists, says Bill Bottke of the Southwest Research Institute's Boulder, Colo., office, had initially conjectured that the solar system grew up in a hurry, "with everything you see today already in place just a few million years after the solar system's birth. But we're now considering the possibility that the solar system literally rearranged itself about 3.9 billion years ago."

At the Lunar and Planetary Institute in Houston last November, theorists and observers convened for a rare meeting in which they hashed out what each had gleaned about the solar system's early history. "We have two communities coming at the same problem from very different perspectives," says Don Bogard of NASA's Johnson Space Center in Houston.

At the meeting, the observers presented new analyses of data first gathered nearly 40 years ago when the Apollo spacecraft landed on the moon and brought back moon rocks--one of the best preserved records of the solar system's tumultuous first 700 million years. Theorists presented their latest version of a theory that could account for several unexplained features of the solar system, including the violent era between 4 billion and 3.9 billion years ago known as the late heavy bombardment, when the planets were pelted with debris. And researchers reported evidence that if life had existed on Earth before that, the cataclysm might not have wiped out all organisms but could have spared primitive forms that thrived in hot, water-rich environments.

Bombardment of data

Many of the new studies focus on events that gave the final touches to the architecture of the solar system--events that took place just a few hundred million years after the planets had coalesced from the primordial disk of gas, dust and ice believed to have swaddled the infant sun. The planet-forming process probably took only a few tens of millions of years, and by 50 million to 60 million years after the birth of the solar system, the orbs had pretty much grown to their present size. …

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