Categories: Astronomy

Watch Asteroid 1998 OR2 Zip Past Earth This Week

A fascinating asteroid named 1998 OR2 pays our neck of the inner solar system a visit early Wednesday morning, and if skies are clear, you might just get a chance to watch it slide by.

The asteroid is 1998 OR2, a 1.2 mile (2 kilometer)-wide space rock. And though the asteroid is on the list of potentially hazardous objects (PHOs), the April 29th pass at 0.042 Astronomical Units (AU) from Earth at 9:56 Universal Time (UT)/5:56 AM Eastern Daylight Saving Time (EDT) poses no threat to the Earth. That’s 6.3 million kilometers miles distant, about 16 times greater than the distance from the Earth to the Moon.

The orbital path of asteroid 1998 OR2. Credit: NASA JPL.

This week’s pass is the closest for the asteroid versus Earth since the discovery of 1998 OR2 by the Near-Earth Asteroid Tracking program (NEAT) based at the Haleakala observatory on the night of July 24th, 1998. Pre-recovery images of the asteroid stretch back to 1987, giving astronomers an observation arc of over 30 years; we know the orbit of this one pretty well. 1998 OR2 is an Amor asteroid, with a perihelion just exterior to the Earth’s orbit. This week’s pass is the second closest for the asteroid to Earth the for the 21st century. The asteroid passes three times closer to our fair planet on April 16th, 2079, when it will pass 0.012 AU or 1.8 million kilometers (11 million miles) from the Earth, about as close as it can get in the current epoch.

Go, tumbling space-rock… Credit: Arecibo/NASA/NSF.

This week’s pass gives astronomers a chance to refine 1998 OR2’s orbit even further. Arecibo radar was busy pinging the asteroid over the past week, painting a picture of its ghostly cratered surface. We also know from radar observations that 1998 OR2 rotates on its axis once every four hours. At a misshapen crescent phase, the asteroid seems to be showing up to the ongoing worldwide pandemic in suitable face mask’d attire:

Arecibo astronomer Anne Virkki and asteroid 1998 OR2. Image courtesy of Anne Virkki.

One day, 1998 OR2 will either get ejected from the inner solar system, or could potentially smack the Earth or Moon, centuries or millennia from now. Such an impact would cause limited regional damage only, similar to the Australasian strewn field event that showered the Pacific region with tektites some 790,000 years ago. Humanity is also busy exploring two other near Earth space rocks of similar size, with JAXA’s Hayabusa 2 spacecraft which departed asteroid 162173 Ryugu this past November, and NASA’s OSIRIS-Rex mission, currently at asteroid 101955 Bennu.

1998 OR2 passing the bright star Mu Hydrae on April 28th. Times are marked in UT, and stars are plotted down to +10th magnitude. Credit: Created by the author using Starry Night Education Software.

Looking skyward, this week sees the asteroid exiting the constellation Sextans into the long meandering constellation of Hydra the Water Snake. The asteroid passes very near the ‘Ghost of Jupiter’ planetary nebula (NGC 3242) on the night of April 28th, and 15’ from the +3.8 magnitude star Mu Hydrae on the same evening.

The celestial path of asteroid 1998 OR2 through the end of April. Credit: Starry Night w/annotations by the author.

At its closest on Tuesday night into Wednesday morning, 1998 OR2 will shine at about magnitude +10, a descent catch for a small telescope. And though the asteroid is headed southward, Hydra is currently well-placed in late April for northern hemisphere observers, high to the south below the astronomical constellation of Leo the Lion immediately after dusk.

The parallax shift for the asteroid as seen from Earth is negligible at 2.5’ at closest approach, and the asteroid will be moving an apparent 2 degrees across the sky once every seven hours, or the span of a Full Moon once every 1 hour and 45 minutes. Use a fine finder chart or planetarium program to locate the asteroid’s star field, and sketch or photograph the suspect star field and watch for the ‘star’ that seems to move slowly out of place. 1998 OR2 should show discernible motion even at low power after about 20-30 minutes of observation.

Asteroid 1998 OR2 (centered). For an animated version, click here. Credit: Gianluca Masi/Virtual Telescope Project

Clouded out? You can still watch the passage of 1998 OR2 past the Earth courtesy of Gianluca Masi and the Virtual Telescope Project, starting a live webcast at 18:00 UT/2:00 PM EDT on April 28th:

This week’s webcast poster. Credit: the Virtual Telescope Project.

Again… don’t believe the internet hype-machine: 1998 OR2 poses no threat to the Earth this week. Simply enjoy the view of the asteroid, either at the eyepiece of a telescope or online. If there’s one thing that’s we’re sure of in these uncertain times, it’s celestial mechanics.

David Dickinson

David Dickinson is an Earth science teacher, freelance science writer, retired USAF veteran & backyard astronomer. He currently writes and ponders the universe as he travels the world with his wife.

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