Rosetta becomes first spacecraft to enter orbit around a comet


August 7, 2014

The Rosetta spacecraft is now in orbit around comet 67P/Churyumov–Gerasimenko (Image: ESA)

The Rosetta spacecraft is now in orbit around comet 67P/Churyumov–Gerasimenko (Image: ESA)

Image Gallery (17 images)

The list of space firsts got a little longer this week. On August 6 at 11:30 am CET, ESA's Space Operations Centre (ESOC) in Darmstadt, Germany received radio signals confirming that Rosetta had begun its approach and was going into orbit around comet 67P/Churyumov–Gerasimenko, making Rosetta the first spacecraft to go into orbit around a comet.

The culmination of a 10-year journey, this marks the start of a year-long mission by Rosetta to study Churyumov–Gerasimenko to gain new insights into the early history of the Solar System, as well as the first attempt to land on a comet in November. The probe has already traveled 6.4 billion km (3.9 billion mi), and is now 450 million km (280 million mi) from Earth, orbiting Churyumov–Gerasimenko as it plummets toward the inner Solar System at about 55,000 km/h (34,000 mph).

Launched in 2004, Rosetta reached Churyumov–Gerasimenko by a circuitous route involving three flybys of Earth, one of Mars, and a long detour out beyond Jupiter as it built up enough speed to catch up to the comet. During this time, it passed close to the asteroids Šteins and Lutetia, and went into a 31-month hibernation to conserve resources until the comet rendezvous.

In January, Rosetta was awakened by a radio signal from mission control and, over the course of several weeks, its scientific instruments were brought back online, including a NASA package that started examining Churyumov–Gerasimenko in June. Since May, the spacecraft has been carrying out a series of 10 critical course corrections, the failure of which would have resulted in the probe flying past the comet with no hope of recovery.

Like most comets, Churyumov–Gerasimenko has an elliptical orbit – in this case, circling the Sun once every 6.5 years as it travels beyond Jupiter and back inside the orbit of Mars. Astronomers believe that comets, which are “dirty snowballs” composed of ice, rock, and dust, are the remnants of the early Solar System and can tell us a great deal about how the planets formed. In addition, many believe that it was from comet impacts that Earth received its water.

During its approach, Rosetta has trained its navcams and OSIRIS camera at the comet, which sent back dramatic pictures of Churyumov–Gerasimenko; revealing it to be craggier and sharper edged than the asteroids and moons previously explored that had been worn down by billions of years of meteor impacts. The most striking feature is a pronounced neck in the comet nucleus, which makes it look a bit like a rubber duck that’s gone a few rounds with a terrier.

Close up of comet 67P/Churyumov–Gerasimenko (Image: ESA)

In addition, ESA says that observations from the Microwave Instrument for the Rosetta Orbiter (MIRO) show that Churyumov–Gerasimenko is losing water at a rate of 300 milliliters (10 oz) per second, and the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) shows that the comet has an average surface temperature of -70° C (-94° F), which means it’s a very dark and dirty snowball that absorbs rather than reflects sunlight.

Rosetta is currently about 100 km (62 mi) from Churyumov–Gerasimenko and will remain in orbit around it for over a year until the comet swings back toward Jupiter. Because the gravity is so low, the spacecraft isn't making neat circles around the comet, but travels in a series of triangular orbits as it nudges closer to the nucleus over the next six weeks. Eventually, it will go into a circular orbit at a distance of 30 km (18 mi).

As it approaches Churyumov–Gerasimenko, Rosetta will scout out five candidate spots to set down the Philae lander for the historic first attempt at landing on a comet. After the final decision is made sometime in October, Philae will leave Rosetta and head for a touchdown on Churyumov–Gerasimenko on November 11.

"Over the next few months, in addition to characterizing the comet nucleus and setting the bar for the rest of the mission, we will begin final preparations for another space history first: landing on a comet," says Matt Taylor, ESA’s Rosetta project scientist. "After landing, Rosetta will continue to accompany the comet until its closest approach to the Sun in August 2015 and beyond, watching its behavior from close quarters to give us a unique insight and real time experience of how a comet works as it hurtles around the Sun.”

The video below contains highlights of Rosetta’s rendezvous with Churyumov–Gerasimenko.

Source: ESA

About the Author
David Szondy David Szondy is a freelance writer based in Monroe, Washington. An award-winning playwright, he has contributed to Charged and iQ magazine and is the author of the website Tales of Future Past. All articles by David Szondy

" Comets are little more than dirty snowballs according to conventional astronomy. Recent findings, however, challenge this assumption.

In 2000, as comet Linear (named after the telescope that discovered it) approached perihelion, strange things began to happen. It brightened by more than 50% in less than fours hours, and threw off large quantities of 'dust', much more than was expected from ice and other volatiles. Then, to cap it all, the Chandra telescope discovered that the 'dirty snowball' was emitting X-rays!

NASA cited a befuddled process called 'charge exchange reaction', which it claimed was first proposed in 1997. As a matter of fact, however, the electric comet theory has been around for more than a century, and it received clarity from Ralph Juergens in the early 1970s. He proposed the Electric Sun model, with the corollary that cometary comas and tails are produced by an electrical exchange between the sun and a comet. The electric comet video from Thunderbolts can be viewed here. "

Daniel Gregory

That is what I call 'calling your shots'. What a fantastic navigational achievement. Wish they had used atomic power source so that it could follow farther and perhaps report on asteroid flyby also.

Ronald Chappell

This is amazingly impressive. The level of accuracy need to achieve a stable orbit around a comet boggles the mind. I can't wait to get more updates from this project.

Siegfried Gust

Another huge leap for mankind. I'm not that nationalistic and I consider this achievement to be a win, but the US got scooped again. This is just another indication that our priorities are wrong and the misguided obcession for cutting taxes is taking us to third rate (and world) status. This is also another demonstration that it's way too early to try to put humans in deep space and a squandering of resources.


Is it just me, or is there something incongruous and potentially quite funny about the complicated maneuvering and calculations required to put a device into orbit around a distant comet, and to then HARPOON that comet? Astounding!

Phil haultain

I love it when a plan comes together!


It is not (yet) accurate to say Rosetta is in orbit. As noted in the ESA link below, Rosetta needs two more maneuvers to achieve an actual orbit in the weak gravity of this object. These operations will take about 6 more weeks. I also wonder about the classification. This object's orbit is only 6.5 years, entirely inside the orbit of Saturn and perihelion is outside Earth's orbit. Why what standard is this a comet and not an asteroid?

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