Baptistina family

Lore & Background

The Baptistina family consists of darkly colored asteroids and meteoroids in similar orbits. Baptistina broke up into thousands of fragments about 80 million years ago. The namesake asteroid, 298 Baptistina, was discovered on 9 September 1890 by Auguste Charlois at the Nice Observatory; the source of its name is unknown. It measures about 13 to 30 kilometres in diameter. Although it has an orbit similar to the Flora family asteroids, Baptistina is an unrelated interloper. Other members include 1696 Nurmela, 2858 Carlosporter, and (7255) 1993 VY1.

It was originally thought that the Baptistina family may consist of uncommon carbonaceous chondrite. In 2006, nine asteroids within the family were given known classifications: three are S-type, two are X-type, two are A/R-type, one is C-type and one is V-type. However, any conclusions taken from this were highly speculative, as very few members were classified, and not even the albedo of the meteors was known at the time. Following the impact of the Chelyabinsk meteor in 2013, a paper showed that shock produced during impact of a large asteroid can darken otherwise bright silicate material. Spectral analysis of the darkly-colored portions of the non-carbonaceous Chelyabinsk meteorite closely matched the color of members of the Baptistina family, showing that a low albedo does not necessarily indicate the composition of the family.

Reader's Guide

The Baptistina family gained widespread attention when, in 2007, it was proposed that chromium concentrations in 66-million-year-old sediment layers at the Cretaceous–Paleogene boundary suggested that the impactor that gouged out Chicxulub Crater and caused the Cretaceous–Paleogene extinction event belonged to the family. Concerns were raised regarding the reputed link, in part because very few solid observational constraints existed of the asteroid or family. One year later, it was discovered that 298 Baptistina does not share the same chemical signature as the source of the Cretaceous–Paleogene boundary. Because of the timeframe, it had also been suggested that the impactor that produced the lunar crater Tycho 108 million years ago was also a member of the group, as well as the Venusian craters Mead, Isabella, Meitner, and Klenova.

In 2011, data from WISE revised the date of the proposed collision which broke up the Baptistina parent asteroid to about 80 million years ago. If correct, this data means it is very unlikely that the K/Pg impactor was part of this family, as it typically takes many tens of millions of years for an asteroid to reach a resonance with Earth and then collide, much more than the 15 million years between this breakup and the collision of the K–T impactor. As a result, the demise of the dinosaurs remains in the cold case files. The family's significance lies in its role as a test case for linking asteroid breakups to terrestrial impact events, and in demonstrating how spectral darkening from shock can complicate compositional interpretation.

Did You Know?

• The Baptistina family contains more than 2500 members.
• The parent asteroid was 170 km across and broke up 80 million years ago.
• It was once proposed as the source of the Chicxulub impactor, but this was disproven in 2011 using WISE data.
• The Chelyabinsk meteorite's dark portions spectrally matched members of the Baptistina family.