We now know that the dinosaurs were wiped off the face of the Earth after an asteroid struck the planet 66 million years ago. But when the American father-son duo of Luis and Walter Alvarez first came up with the idea in 1980, their listeners were sceptical to say the least.
This, despite the fact that Luis Alvarez was a winner of the Nobel Prize in Physics in 1968 and his son Walter was an expert in geology. The Alvarez hypothesis, which posited that the mass extinction of dinosaurs was caused by the impact of an asteroid on Earth, sounded anywhere from incredible to impossible to most listening to it.
The idea of an asteroid whooshing past close to Earth, let alone hitting the planet, was still alien to many. This, despite the fact that another asteroid repeatedly kept coming close to Earth. On many occasions, however, it kept going unnoticed.
Moves fast
It wasn’t always the case though. On October 28, 1937, German astronomer Karl Reinmuth of Hiedelberg noticed a streak of light in a picture he had taken of the night sky. Reinmuth, a prolific discoverer of hundreds of minor planets, realised that it was an asteroid that was close to Earth and moving fast. So fast, in fact, that he named it Hermes, after the ancient Greek messenger of the Olympian gods.
By October 30, it had come even closer – just about twice as far away from the Earth as the moon is. Reinmuth kept observing it for five days as it raced past the sky, only to then lose it completely.
Goes undetected
For the decades that followed, Hermes remained undetected. This was the case even though it approaches Earth’s orbit twice every 777 days. While the planet is usually far when the orbit crossing occurs, Hermes definitely came close to Earth in 1937, 1942, 1954, 1974, and 1986. While a world obsessed over World War II might have missed out the 1942 encounter, there isn’t sufficient reason to explain the others.
This image show the recovery of Hermes by Brian Skiff on October 15, 2003. | Photo Credit: Photo: Brian A Skiff, Lowell Observatory / Wikimedia Commons
We now know about these other close shaves after Lowell Observatory astronomer Brian Skiff rediscovered Hermes on October 15, 2003. After appearing as a faint speck of light in photos made by the Lowell Observatory’s Near-Earth Object Search programme, it was linked to the observations from 1937.
Binary asteroid
Once the orbit was determined, it was possible to trace it back in time to find out the unidentified flybys. Radar observations following the rediscovery showed that Hermes actually is a binary asteroid. It has two asteroids – each over 500 m across – orbiting each other.
Hermes’ orbit is among the most eccentric of near-Earth asteroids. Apart from being tugged by Earth’s gravity when it comes in its proximity, it is also tugged by Venus’ pull as well as it has close encounters with our neighbouring planet too. In fact, in 1954, Hermes flew by both Earth and Venus. These tugs alter Hermes’ path so much that it is difficult for astronomers to predict it for more than a century in advance.
While predicting Hermes’ path in the distant future is difficult owing to its chaotic orbit, scientists have determined that it won’t get closer than 3 million km in the 100 years or so following its rediscovery in 2003. Hermes’ next closest approach will be on April 25, 2040, when it will pass about 4.2 million km from Earth.
Oh, and in case you are wondering if Hermes, or any other near-Earth object for that matter, might do to us what an asteroid did to dinosaurs, we are already working on a solution. NASA’s DART (Double Asteroid Redirection Test) mission, aimed at testing a method of planetary defence, recently confirmed that its impact was able to change an asteroid’s motion in space.
Published - October 30, 2022 12:08 am IST
