Earth Has An Almost-Moon

Earth has a new quasi-moon: an asteroid called 2016 H03. (Not shown) Image: NASA

Earth has a small companion that NASA is calling an almost-Moon. The small asteroid, called 2016 H03, isn’t quite a moon because it’s actually orbiting the Sun. In its orbit around the Sun, it spends about half of its time closer to the Sun than the Earth.

2016 H03 is called a “quasi-moon” or a “near-Earth companion”. It doesn’t quite qualify as a moon because of its orbit.

Paul Chodas is the manager of NASA’s Center for Near-Earth Object (NEO) Studies at the Jet Propulsion Laboratory in Pasadena, California. He had this to say about 2016 H03: “Since 2016 HO3 loops around our planet, but never ventures very far away as we both go around the sun, we refer to it as a quasi-satellite of Earth.”

2016 H03’s orbit is tilted relative to Earth’s, and it passes through the plane of Earth’s orbit. Over the decades, it also performs a slow, back and forth twist. NASA describes 2016 H03’s orbit as a game of leap frog.

“The asteroid’s loops around Earth drift a little ahead or behind from year to year, but when they drift too far forward or backward, Earth’s gravity is just strong enough to reverse the drift and hold onto the asteroid so that it never wanders farther away than about 100 times the distance of the moon,” said Chodas. “The same effect also prevents the asteroid from approaching much closer than about 38 times the distance of the moon. In effect, this small asteroid is caught in a little dance with Earth.”

Earth’s little quasi-moon has been in its stable orbit for about a century, according to calculations, though it was only spotted on April 27th, 2016, by the Pan-STARRS 1 asteroid survey telescope in Hawaii. Pan-STARRS 1 is operated by the University of Hawaii’s Institute for Astronomy and NASA’s Planetary Defense Coordination Office. (Did you know we had a Planetary Defense Coordination Office?)

2016 H03 is small. It’s exact size has not been established, but it’s between 40 and 100 meters (120 and 300 ft.) It’s been around a century, and calculations say it will be around for centuries more.

2016 H03 is not quite unique. Earth has had other dance partners like it.

“One other asteroid — 2003 YN107 — followed a similar orbital pattern for a while over 10 years ago, but it has since departed our vicinity. This new asteroid is much more locked onto us. Our calculations indicate 2016 HO3 has been a stable quasi-satellite of Earth for almost a century, and it will continue to follow this pattern as Earth’s companion for centuries to come,” said Chudas.

NASA tracks thousands of NEOs and assesses their risk of collision with Earth. Though 2016 H03 is an interesting specimen because of its orbit, it poses no threat to Earth.

Comet Pan-STARRS Wows Over Holland

Comet Pan-STARRS thrills Dutch observers of the Night Sky on March 14, 2013 shortly after sunset- note the rich hues. Shot with a Canon 60D camera and Canon 100/400 mm lens, exposure time 2 seconds, ISO 800. Credit: Rob van Mackelenbergh
See viewing guide and sky maps below
Update – see readers photo below[/caption]

Comet Pan-STARRS (C/2011 L4) is exciting amateur astronomers observing the night sky worldwide as it becomes visible in the northern latitudes after sunset. And now it’s wowing crowds in Europe and all over Holland – north to south.

Check out the beautiful, richly hued new photos of Comet Pan-STARRS captured on March 14, 2013 by Dutch astrophotographer Rob van Mackelenbergh.

“I took these photos in the southern part of the Netherlands on Thursday evening, March 14, at around 7:45 pm Dutch time with my Canon 60 D camera.”

“I was observing from the grounds of our astronomy club – “Sterrenwacht Halley” – named in honor of Halley’s Comet.”

Comet Pan-STARRS is a non-periodic comet from the Oort Cloud that was discovered in June 2011 by the Pan-STARRS telescope located near the summit of the Hawaiian Island of Maui.

The comet just reached perihelion – closest approach to the Sun – on March 10, 2013. It passed closest to Earth on March 5 and has an orbital period of 106,000 years.

Comet Pan-STARRS from Holland on March 15, 2013 at about 7:45 PM, shortly after sunset - Canon 60D camera, Canon 100/400 mm lens, exposure time 15 seconds, ISO 300.   Credit: Rob van Mackelenbergh
Comet Pan-STARRS from Holland on March 14, 2013 at about 7:45 PM, shortly after sunset – Canon 60D camera, Canon 100/400 mm lens, exposure time 2 seconds, ISO 800. Credit: Rob van Mackelenbergh

“Over 30 people were watching with me and they were all very excited, looking with binoculars and cameras. People were cheering. They were so excited to see the comet. But it was very cold, about minus 2 C,” said Mackelenbergh.

The “Sterrenwacht Halley” Observatory was built in 1987 and houses a Planetarium and a Celestron C14 Schmidt-Cassegrain telescope. It’s located about 50 km from the border with Belgium, near Den Bosch – the capitol city of southern Holland.

Comet Pan-STARRS was photographed from Sterrenwacht Halley - or 'Halley Observatory' in Holland.  Credit: Rob van Mackelenbergh
Comet Pan-STARRS was photographed from Sterrenwacht Halley – or ‘Halley Observatory” in Holland. Credit: Rob van Mackelenbergh

“It was hard to see the comet with the naked eye. But we were able to watch it for about 45 minutes altogether in the west, after the sun set.”

“The sky was completely clear except for a few scattered clouds near the horizon. After the comet set, we went inside the observatory for a general lecture about Comets and especially Comets Pan-STARRS and ISON because most of the people were not aware about this year’s pair of bright comets.”

“So everyone was lucky to see Comet Pan-STARRS because suddenly the sky cleared of thick clouds!”

Comet Pan-STARRS from Holland on March 15, 2013 at about 7:45 PM, shortly after sunset - Canon 60D camera, Canon 100/400 mm lens, exposure time 15 seconds, ISO 300.   Credit: Rob van Mackelenbergh
Comet Pan-STARRS from Holland on March 14, 2013 at about 7:45 PM, shortly after sunset – Canon 60D camera, Canon 100/400 mm lens, exposure time 2 seconds, ISO 800. Credit: Rob van Mackelenbergh

“In the past I also saw Comet Halley and Comet Hale-Bopp, but these are my first ever comet photos and I’m really excited !”

“I hope to see Comet Pan-STARRS again in the coming days when the sky is clear,” Mackelenbergh told me.

Over the next 2 weeks or so the sunset comet may grow in brightness even as it recedes from Earth into darker skies. Right now it’s about magnitude 0.2.

So keep looking with your binoculars; look west for up to 1 to 2 hours after sunset – and keep your eyes peeled.

And report back here !

Ken Kremer


See a readers photo of sunset Comet Pan-STARRS below

Comet Pan-STARRS viewing graphic from NASA
Comet Pan-STARRS viewing graphic from NASA
Comet Pan-Starrs Sky Map. Viewing guide to find the comet low in the horizon after sunset.Credit: Space Weather.com
Comet Pan-Starrs Sky Map. Viewing guide to find the comet low in the horizon after sunset.Credit: Spaceweather.com