Asteroid the size of a skyscraper here to make your Halloween super scary

Asteroid PHA 2022 RM4 will make its closest approach to Earth either tomorrow or the day after tomorrow, depending on your time zone. As asteroid encounters go, it’s not particularly close, passing us within 2.3 million kilometers (1.43 million miles), or six times the distance of the Moon. There are, however, aspects of this event that make it stand apart from its time.

The first is that PHA 2022 RM4’s orbit crosses ours, so one day it could actually hit Earth, hence the PHA (Potentially Hazardous Asteroid) designation. Plus, it’s big enough to cause serious damage if it hits Earth, though it’s certainly no dinosaur killer. Somewhere between 330 and 740 meters (1,080-2,430 feet) in diameter, this is not an object to be measured in African wildlife. Once we get a more accurate estimate of its size, everyone will be able to check if it’s longer than the tallest building in their city. At present, only a few cities have buildings so tall that they can be confident of overcoming it.

Perhaps the most disturbing thing about the PHA 2022 RM4, however, is in the middle part of its name. We only discovered this object in September this year. All hopes that we had discovered all the short-period asteroids with Earth-transit orbits longer than about 300 meters (980 feet) have now been dashed. Instead, we must accept that the possibility of a large space rock unexpectedly striking our planet at night remains a distinct possibility.

Projects like DART to deflect objects capable of unleashing massive tsunamis or blackening the skies for months are all very well if we have plenty of warning, but of little use with less than two months notice.

With an orbit of 1,400 days (3.8 years), PHA 2022 RM4 spends most of its time further from the Sun than Mars, but its closest approach is just inside Earth’s orbit. It is unusual how far from the planetary plane its orbit is.

No closest approaches to Earth have been calculated, so PAH 2022 RM4 is not a threat for the foreseeable future. However, on a trajectory like this it is likely to eventually become a problem that needs to be addressed.

Gianluca Masi of the Virtual Telescope Project managed to capture the below image of PHA 2022 RM4 as a tiny dot two days before its closest approach. The telescope tracked the asteroid as it moved across the sky, making the background stars appear as lines. At the time, the object was almost exactly twice its closest distance to Earth.

PHA 2022 RM4 as imaged by the Virtual Telescope Project two days before its closest approach. Image credit: Gianluca Masi, Ceccano (FR), Italy – MPC: 470 – The Virtual Telescope Project

The Virtual Telescope Project will be back in action tracking the asteroid during its closest approach on November 1, starting at 17:00 UTC.

Under dark skies, skilled observers may be able to pick it up themselves using medium-sized backyard telescopes, although it will be too far south for many Europeans and North Americans.

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