The Crestone Eagle • November, 2021

Skies Over Crestone: November 2021

by Kim Malville

November 7: End of daylight-savings! Take time to look to the west-southwest to see the young crescent moon close to Venus just left of the constellation of the Teapot otherwise known as Sagittarius.

November 9: Look for the line of the crescent moon, Jupiter, Saturn stretching some 25° along the southern horizon. And don’t forget brilliant Venus soon after sunset

November 10: The moon, Saturn and Jupiter form a triangle in Capricorn.

November 19: The full moon lies between the Pleiades and the Hyades.

Lucy in the Sky with Diamonds

This story starts with a searing hot day in the dry hills of the Afar, a dangerous region of Ethiopia, noted for dangerous animals and fierce nomads with a reputation for castrating and killing intruders. On November 24, 1974, during a period of relative calm in Ethiopia, Donald Johanson and student Tom Gray found several hundred fragments of a fossil skeleton, appearing to be human and very old.  While they were reconstructing the skeleton in their desert tent, they listened to the Beatles song “Lucy in the Sky with Diamonds”. They named her Lucy, having lived at a time close to our origin on the earth, 3.2 million years ago. Two books by Johanson followed that discovery: Lucy, the Beginnings of Humankind in 1981, and almost like a movie sequel, Lucy’s Child, the Discovery of a Human Ancestor in 1989. Lucy, the best known member of her species of hominids, Australopithicus afarensis, may have tragically died from falling 40 feet out of a tree while sleeping.

“Cousin” Lucy – many times removed.
reconstruction by John Gurche

Jump ahead to October 16, 2021, when a robotic space million named Lucy was launched from Cape Canaveral to explore two clusters of asteroids, known as Trojans, which travel around the sun ahead of and behind the greatest planet in the solar system, Jupiter. They lie in two stable regions, known as Lagrange points, some 230 miles ahead of and behind Jupiter. These Trojans are not like the rocks in the asteroid belt, between Jupiter and Mars, which may be the remains of an attempt to create planet too close to massive Jupiter. 

Lucy will spend 6 years visiting asteroids in these two clusters of very old rocks. One the way to the Trojans, Lucy will visit an asteroid in the asteroid belt named Donaldjohanson. The discoverer of Lucy is now a paleoanthropologist now at the Institute of Human Origins at Arizona State University. After watching the launch of Lucy, Johanson says he will never again look at Jupiter the same way he did before. As he described his feelings, to realize his fossil’s namesake is on the way to Jupiter and its Trojans is something utterly and totally unanticipated in his life.

Over 12 years, Lucy will travel nearly 4 billion miles moving at about 400,000 miles per hour. Pretty good for an australopithecine! Lucy will fly by the asteroids at about 15,000 miles per hour, about four times slower than when NASA’s New Horizons spacecraft zipped by Pluto. Furthermore, Lucy will also be a mere 600 miles away from each asteroid during its flyby. That means that pictures of the Trojan asteroids will have great clarity, undoubtedly giving us new puzzles to figure out. Lucy, representing the youth of our species, is going to teach us about the youth of our solar system. 

NASA’s spacecraft OSIRIS-REx rendezvoused with Bennu, an asteroid orbiting the sun more than 200 million miles from Earth, in late 2018. Since then, the spacecraft has studied the object in more detail than any other asteroid in the history of space exploration. Bennu belongs to a class of smaller bodies that scientists call “rubble pile” asteroids, loosely held-together mounds of debris. This pile of loosely held-together rocks is as wide as the Empire State Building is tall.

Bennu rubble pile. photo courtsy of Nasa

Using OSIRIS-REx’s own navigational instruments and other tools, Profesor Dan Sheeres at the University of Colorado, together with his colleagues, spent nearly two years mapping the structure of Bennu’s gravity field.  When OSIRIS-REx first arrived at Bennu, they observed tiny bits of material, some just the size of marbles, which seemed to pop off the asteroid and into space. In many cases, those particles circled Bennu before falling back down to the surface. They watched those particles very closely as they moved outward and inward. It was a little like someone was on the surface of the asteroid, throwing these marbles up so they could be tracked. The gravity field of the asteroid could be inferred from the trajectories of those particles. 

Combining those records of Bennu’s gravity, combined with precise measurements of how the asteroid tugged on the spacecraft over a period of months, it was possible to study the core of the asteroid. The team discovered the presence of vacancies near its center. Such a void at its center could be large enough to contain a couple of football fields. The asteroid has a rotational rate of 4.3 hours, and its spin may be responsible for that void. It is spinning fast due to the effect of sunlight on its surface. That increasing momentum could be slowly pushing material away from the asteroid’s center and toward its surface.  Bennu may spin itself to pieces in a few million years.

Route of Lucy to the Trojan Asteroids. photo courtesy of Nasa

But before that happens, Bennu has a 1/1800 chance of impacting Earth. Venus could also be hit, but if Earth becomes the target, a collision could occur between 2178 and 2290. If all of its matter stays together, the energy of the event could be greater than the collision that occurred 65 million years ago which exterminated many life forms, including dinosaurs. 

If Bennu is on a collision course with us, will it be possible to nudge such a loosely held-together rubble pile away from Earth? Perhaps it will result in the most brilliant meteor shower ever witnessed by humans, but it will not be without danger, with rocks the size of houses and horses falling from the sky. The event may not result in the end of civilization, but it will not be your grandmother’s meteor shower.