Searching for the Origins of the Dinosaur-Killing Asteroid
Scientists think that a giant asteroid, which broke up long ago in the main asteroid belt between Mars and Jupiter, eventually made its way to Earth and led to the extinction of the dinosaurs. Data from NASA's WISE mission likely rules out the leading suspect, a member of a family of asteroids called Baptistina, so the search for the origins of the dinosaur-killing asteroid goes on. This artist's concept shows a broken-up asteroid. NASA/JPL-Caltech

The Baptistina family of asteroids has just been ruled out in the 65-million year-old cold case surrounding the mysterious death of Earth's dinosaurs, leaving scientists to now ask 'Who did it?'

It is a widely held belief in science that a large asteroid had crashed to Earth some 65 million years ago, taking the lives of dinosaurs and other terrestrial life forms on the planet. But where that asteroid came from and how it found its way to Earth is still unknown by scientists.

Then in 2007, a study conducted using visible-light data from ground-based telescopes made the suggestion that the trace of a huge asteroid known as Baptistina was a possible suspect.

The Baptistina family is an asteroid family likely formed by the breakup of an asteroid 170 kilometers (110 miles) across 80 million years ago. This is following an impact with a smaller body. The largest presumed trace of this parent asteroid is 298 Baptistina.

Scientists believe many mountain-sized fragments from the collision would've leaked into the inner solar system through orbital resonances with Mars and Jupiter, which caused a prolonged series of asteroid impacts between 100 and 50 million years ago. Orbital resonances occur when two orbiting bodies exert a regular, periodic gravitational influence on each other. It greatly enhances the mutual gravitational influence of the bodies, that is, their ability to alter or constrain each other's orbits.

Simply put, resonances are areas in the main belt where gravity nudges from Jupiter and Saturn can act like a pinball machine that flings asteroids out of the main belt and into the region near Earth.

Scientists believe that one of those pieces may have impacted Earth and cause the dinosaurs' demise.

Not so, says NASA.

In fact, data from the NASA's Wide-field Infrared Survey Explorer (WISE) has revised the date of the proposed collision that destroyed the Baptistina parent to about 80 million years ago. And if this is correct, the data would not only exclude Baptistina as the culprit, but also revise a number of other impacts previously associated with this asteroid family.

WISE is a NASA infrared-wavelength astronomical space telescope launched on Dec. 14, 2009. It was a replacement for the Wide Field Infrared Explorer (WIRE), which had failed within a short time of reaching orbit in March 1999.

WISE is over 1,000 times more sensitive than prior infrared space surveys in certain measurements. It was hibernated on Feb. 17 this year when its transmitter was turned off.

As a result of the WISE science team's investigation, the demise of the dinosaurs remains in the cold case files, said Lindley Johnson, program executive for the Near Earth Object (NEO) Observation Program at NASA Headquarters in Washington. The original calculations with visible light estimated the size and reflectivity of the Baptistina family members, leading to estimates of their age, but we now know those estimates were off. With infrared light, WISE was able to get a more accurate estimate, which throws the timing of the Baptistina theory into question.

A year of survey

According to NASA, WISE surveyed the entire celestial sky twice in infrared light between January 2010 and February 2011.

NEOWISE, commonly known as the asteroid-hunting portion of the mission, used that same data to catalogue more than 157,000 asteroids in the main belt. They also discovered more than 33,000 new ones, according to NASA.

Since visible light will reflect off an asteroid without knowing how reflective the surface of the asteroid is, it is difficult to accurately establish size.

Infrared observations however, allow a more accurate size estimate, as they detect infrared light coming from the asteroid itself. This is related to the body's temperature and size, NASA said. And once the size is known, the object's reflectivity can be re-calculated by combining infrared with visible-light data.

Calculating Baptistina

The NEOWISE team then measured the reflectivity and the size of about 120,000 asteroids in the main belt to include 1,056 members of the Baptistina family.

The scientists also calculated that the original parent Baptistina asteroid actually broke up closer to 80 million years ago, half as long as was originally proposed.

NASA said this calculation was made possible because the size and reflectivity of the asteroid family members show how much time would've been required to reach their current locations. Larger asteroids wouldn't scatter in their orbits as fast as smaller ones.

The results therefore, revealed that a chunk of the original Baptistina asteroid needed to hit Earth in less time than previously believed, in just about 15 million years, in order to cause the extinction of the dinosaurs as we know it.

This doesn't give the remnants from the collision very much time to move into a resonance spot, and get flung down to Earth 65 million years ago, said Amy Mainzer, a co-author of a new study.

The study will be published in the Astrophysical Journal.

Mainzer is also the principal investigator of NEOWISE at NASA's Jet Propulsion Laboratory (JPL) in Pasadena. Calif.

This process is thought to normally take many tens of millions of years, she added.

Therefore, the asteroid family that created the dinosaur-killing asteroid is at large.

In the Gulf of Mexico, there is evidence that a 10 kilometer (about 6.2-mile) wide asteroid impacted Earth 65 million years ago, causing a huge, crater-shaped structure and rare minerals in the fossil record. These minerals are said to be common in meteorites, but rarely found in Earth's crust.

Plenty of dinosaurs lived at the time of their demise

A 2004 research on the analysis of global fossil records by a team of researchers led by a University of Rhode Island paleontologist showed that when dinosaurs became extinct because of effects from a massive asteroid, there were more varieties of the reptiles living than ever before.

David Fastovsky, URI professor of geosciences, at the time said the analysis finally rested the old, utterly unsupported idea that dinosaurs were declining in diversity during the last 10 million years of their time on Earth.

The researchers then found that early dinosaurs from the late Triassic period comprised only 40 known genera, but diversity dramatically increased throughout the time dinosaurs were on Earth, skyrocketing in the Cretaceous period -? 99 to 65 million years ago -? when at least 245 dinosaur genera lived.

The NEOWISE team also found various main belt asteroid families have similar reflective properties, and they hope to use data to separate families that overlap and trace their histories.

We are working on creating an asteroid family tree of sorts, said Joseph Masiero, the lead author of the study. We are starting to refine our picture of how the asteroids in the main belt smashed together and mixed up.