Credit: www.tickreel.com
There are many theories behind the extinction of dinosaurs 65 million years ago. One theory is that an impact of an asteroid causes it but no one is sure what type or how the asteroid heads to the Earth. From the study in 2007 by using data from observatories in visible-wavelength range, the culprit is the type of asteroid called "Baptistina."
From the theory, Baptistina is hit with another smaller asteroid in the belt between Mars and Jupiter around 160 million years ago. The impact sent pieces of fracture, which could have a size of mountains, and they are believed to strike on Earth and cause the extinction. Since the theory was proposed, more and more evidence show that the Baptistina family of asteroid is unlikely the culprit. Moreover, the recent Wide-field Infrared Survey Explorer (WISE) suggests that we could eliminate this theory.
Sizes and reflecting abilities of the Baptistina family are determined using visible light in previous studies which leads to the estimation of their age. However, WISE says that those estimations are not precise. Since WISE use infrared, it could provide a much more accurate estimation which make the Baptistina theory in a big trouble.
WISE did the survey twice since January 2010 until February 2011. A part of the survey, called NEOWISE, is to find asteroids. It makes a list of more than 157000 asteroids in the asteroid belt and has found more than 33000 new asteroids.
In order to determine the size of an asteroid, with out the reflecting ability of that asteroid, it is hard to do with visible light. The survey in infrared should help an accuracy of the estimation. From infrared which gives details about an object's temperature and size, astronomers could use size and visible-range data to find the reflecting ability of the object.
The NEOWISE team studies the reflecting ability and size of more than 120000 asteroids including 1056 Baptistina asteroids. They estimate the breaking time (from hitting with another asteroid) should be around 80 million years ago or only half the time estimated before. The calculation used nowadays size and reflecting ability to find how long it takes to travel from impact site to where it is now. Moreover, large pieces will on spread as fast as the smaller pieces. From this calculation, the Baptistina asteroid only have 15 million years to travel to the Earth to kill the dinosaurs. That amount of time is not enough for an asteroid to move into the resonant area and head to Earth. The mechanism should take at least 50 million years. The resonant area is a part of an asteroid belt that gravity from Jupiter and Saturn act as a pinball machine that kicks asteroids from their course to Earth.
Other types of asteroid might cause the extinction too since there are evidences for an impact of 10-kilometer-wide asteroid hit the Earth 65 million years ago - a structure similar to a crater in a bay of Mexico, and rare elements in fossil record which are abundant in asteroids.
This news remind me of this comic from SMBC.
Haha, I love the comic!
ReplyDeleteDid the article mention how the reflecting ability of the asteroids allows us to figure out where they came from how long ago? That sounds like a really tricky problem to work out.
What defines the Baptistina class of asteroids and what made people initially think that they had caused the mass extinction?
They assume that pieces with the same reflecting ability are broken from a larger piece. So, they track the trajectories back and determine how long since the asteroids broke off.
ReplyDeleteThe theory about the Baptistina can be found at Nature "An asteroid breakup 160 Myr ago as the probable source of the K/T impactor." [www.nature.com/nature/journal/v449/n7158/full/nature06070.html]
In the paper, the terrestrail and lunar cratering rate is constant for over the past 3 Gyr. However, the impact rate is twice higher in the past 100 Myr. So, they assumed that the surge was caused by the catastrophic disruption of the parent body of the asteroid Baptistina.