A 'dark object' may have brought life to Earth

An elusive class of objects may be much more numerous than previously thought and may be life-bearing spacecraft.

A research team led by astrophysicist Darryl Seligman from Michigan State University (USA) has discovered seven new elusive objects, which are known by the nickname "dark comets".

Illustration of an object known as a "dark comet" - (Photo: NICOLE SMITH/UNIVERSITY OF MICHIGAN).

Dark comets have the characteristics of asteroids but behave similarly to comets, so it is impossible to clearly distinguish which of the two basic types of astronomical objects they are.

The seven newly discovered dark comets bring the total number of dark comets known to mankind to 14. And that's not all.

American scientists believe they are more numerous than we think, come in two varieties and play a very special role in our world today.

"These objects represent a class of objects in the solar system that may have provided Earth with materials necessary for the development of life, such as volatiles and organics," said Dr. Seligman.

Because dark comets do not have tails like normal comets, the clearest evidence to identify them is the acceleration of these objects as they move through space.

What makes these objects accelerate through space without sublimation could be gravity or the Yarkovsky effect, says co-author Davide Farnocchia, an astronomer at NASA's Jet Propulsion Laboratory (JPL).

The Yarkovsky effect is a change in orbit caused by contrasts in light and temperature. When an object is exposed to sunlight, some of the light energy is absorbed, heating the object's surface and generating thermal emission in the form of photons.

By analyzing reflectivity and orbits, the authors also discovered that our solar system contains two different types of dark comets.

One species lives in the inner region of Mars' orbit. They tend to be smaller, less than a few tens of meters across, with compact, circular orbits around the Sun.

The other type is a bit more chaotic. Their orbits are elongated elliptical, moving as far away from the Sun as Jupiter and sometimes closer than Mercury.

They are also larger than the first type, reaching sizes of up to hundreds of meters.

In addition, it is very possible that dark comets from other star systems have also visited us, such as Oumuamua - which is debated to be an asteroid or an extraterrestrial spacecraft - is an example.