Surprise Asteroid Zips Very Close to Earth, Grazing Path of Satellites in Geostationary Orbit

A reasonably small 4-8 m asteroid recently flew by Earth, passing close to satellites orbiting in the geostationary ring at a distance of about 42,735 km from Earth’s center and only about 1200 km from the nearest satellite.

After the initial discovery, observers around the world rapidly set their eyes on the ‘new’ space rock, determining it would safely pass our planet in one of the closest flybys ever recorded.

While the asteroid, now named 2020 HS7, came close to the geostationary ring, it passed ‘under’ the nearest satellite and posed no major risk as their orbits did not intersect.

PanSTARRS1 Observatory on Haleakala, Maui just before sunrise. Credit: Rob Ratkowski / PS1SC

UFO spotted in Hawaii

On the evening of April 27 (European time), NASA’s Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) in Hawaii reported observations of a new asteroid, temporarily labeled P20ZIf8.

The night before, one of the Pan-STARRS survey telescopes had spotted an unidentified object flying through space. Less than an hour of observations showed that this object was already extremely close to Earth, with a roughly 10% probability of collision the following day.

Rapid global response deems asteroid small and safe

Observers around the world quickly joined the effort to find out more about this unknown asteroid. Only 50 minutes after the initial Pan-STARRS report was released, the Xingming Observatory in China obtained the first follow-up ‘astrometry’ — data on its position, motion, and brightness.

Soon after, the Tautenburg observatory in Germany – a frequent collaborator with ESA’s Near-Earth Object Coordination Centre, part of the Planetary Defence Office – monitored the space rock, after the Agency alerted them to it and asked for immediate observations.

Orbit trajectory of asteroid 2020 HS7 during its close Earth fly-by on April 28, 2020. Credit: ESA

With this data, it became clear that the object was not going to collide with the Earth, but it was heading towards a very close fly-by the following day, roughly at the distance of Earth’s geostationary ring.

At just a few meters in size, ‘P20ZIf8’ would not have caused any significant threat if it had been on a collision course, as it would likely have burned up in Earth’s atmosphere.

Despite posing no threat to Earth, the detection, follow-up and characterization of this new asteroid was an interesting exercise, testing the discovery and rapid follow-up capabilities of observers worldwide.

One of the closest asteroids to fly by

Subsequent observations obtained by additional ESA collaborators and many other observatories worldwide determined that the flyby of the asteroid, now named 2020 HS7, ranks among the 50 closest ever recorded.

We now know with a precision of just a few kilometers and a few seconds, that the flyby occurred on April 28 at about 18:49:40 UTC (20:49:40 CEST), at a distance of about 42,745 km from Earth’s center. 

Plots representing the orbit of asteroid 2020 HS7 in its close Earth fly-by on the 28 April 2020: on the left, the orbit as seen from the Ecliptic North Pole, on the right as it seen on the Ecliptic plane, crossing it with an angle of ~10 degrees. Credit: ESA

That these numbers are so precise, shows that the trajectory of a nearby object can be established with exquisite accuracy even with just a day’s worth of data, if good observational coverage can be obtained.

Interestingly, the fly-by happened only 15 hours before the closest approach of (52768) 1998 OR2, a much larger kilometer-sized object that attracted the attention of the worldwide media. However, this latter object approached our planet at a distance 16 times farther than the Moon (more than 6 million kilometers away), while 2020 HS7 came significantly closer to us, representing a more significant event for the astronomical community.