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For the first time, ever, humanity has put a robotic lander down on the surface of a comet. It's a history-making event, but when it comes down to it, why? Find out inside.

Rosetta Mission: Everything you need to know about this historic comet chase and landing

Scott Sutherland
Meteorologist/Science Writer

Wednesday, November 12, 2014, 7:43 PM - The European Space Agency is reporting the incredible success of its Rosetta mission, after landing a robot packed with scientific instruments on the surface of a comet for the first time in human history.

Here is a rundown of the details of this amazing journey, the science the mission has already collected, what's to come in the future, and why it's all so important to us here on Earth.

A journey by the numbers

  • 21 years in the making, since the concept of the mission was first laid out
  • 10+ years in space, on a wide looping orbit to chase down Comet 67P/Churyumov-Gerasimenko
  • 4 gravity-assist maneuvers: 3 from Earth, 1 from Mars
  • 2 asteroid flybys: Steins in 2008 and Lutetia in 2010
  • 31 months in hibernation
  • 3+ months in orbit of the comet, investigating its environment and looking for landing sites
  • 1 day of final checks to ensure that Rosetta and Philae were ready for the next important step
  • 7 hours of landing as Philae descended to the comet's surface
  • 500 million kilometres distance between Earth and Comet 67P
  • 28-minute communication delay causing immeasurable stress to the mission team!

RELATED: Five awesome facts you may not know about the ESA's Rosetta comet mission

A pair of intrepid explorers

Rosetta orbiter and instruments (Credit: ESA)

Philae lander and instruments (Credit: ESA)

Rosetta was not only designed to chase down 67P/Churyumov-Gerasimenko and orbit the comet, she was also designed with her own science investigations in mind. Nearly a dozen different instruments bristle from the spacecraft, most of which have already been returning some incredible results to the scientists back here on Earth.

Philae was along for the entire ride with Rosetta, from launch on March 2, 2004, up until 4:03 a.m. ET, November 12, 2014, but this dishwasher-sized lander has captured most of the attention over the past day. With an array of 10 instruments of his own, Philae is key to getting as much science out of this mission as possible, as he will examine the comet, up-close, from the surface.

RELATED: Rosetta spacecraft snaps an interesting shot of a comet

An ambitious target

Comet 67P/Churyumov-Gerasimenko is a massive chunk (or two chunks!) of ice and rock that makes a regular journey around the Sun, taking it from between the orbits of Earth and Mars out to beyond Jupiter and back, roughly every 6.5 years. Believed to originate from the Kuiper Belt, out beyond the orbit of Neptune, it was likely knocked towards the inner solar system by some kind of collision, and was trapped in its current orbit by Jupiter's immense gravitational pull. Estimated at around 10 trillion kilograms total, and measuring over 4 kilometres wide along its larger 'lobe' and about 4.5 kilometres long from end to end, this comet would strike an imposing shadow over any location on Earth (if it ever got that close).

As dramatic as that image is, this comparison of Comet 67P to the city of Toronto (inspired by similar images produced by the ESA featuring various European cities) would never happen in real life. The closest Comet 67P ever gets to Earth is around 36 million kilometres, or nearly 100 times further away than the Moon, so we're perfectly safe from such a scenario.

RELATED: ESA picks landing site for Rosetta's Philae lander - 'J' marks the spot!

A historic landing

Credit: ESA

The timing of this landing went off without a hitch. Separating from Rosetta at 4:03 a.m. ET on Wednesday, Philae descended to the surface of the comet, landing exactly 7 hours later, at 11:03 am EST. However, although that portion of the process went as planned, there is some uncertainty about the stability of the landing. Technical difficulties involving Philae's rockets and harpoons, as well as an anomalous spin as the lander descended, added complications to the process.

As of now, it's still unclear if the lander has a solid grip on the comet.

The ESA mission team reports that they're in intermittent communication with the lander, and will be working to find out more (and potentially solve the problem if it presents a threat to the mission).

Hopefully Philae remain in operation as planned to gather science over the next few months.

RELATED: Landing on a comet is 'ridiculously hard' and you can try it out for yourself!

Did anything cool happen during the landing?

Although we had to wait awhile for results of Philae's descent to the surface of the comet, just after the lander separated from Rosetta, they both gave us a treat.

Rosetta snapped an image of Philae as he moved away towards the comet.

While Philae turned his camera back towards Rosetta and captured a parting image of its partner.

RELATED: Rosetta mission reports successful landing after nail-biting wait, but lander stability remains in question

Okay, but there has to be something cooler than that about this comet

Indeed there is!

Credit: ESA/Rosetta/NavCam

Ever since Rosetta arrived at the comet, it has been 'listening' in with a special magnetometer instrument. Mission scientists hadn't expected to find this, but they discovered that the comet was putting off magnetic signals, that when they converted to soundwaves, produced a strange kind of music. There's some speculation that these magnetic pulses originate from the material streaming off the comet, as it interacts with the Sun's solar wind, but at the moment, the science team really isn't sure how this is happening!

RELATED: Comet 67P/Churyumov-Gerasimenko sings, and Rosetta mission scientists aren't sure why!

What has the mission found so far?

Rosetta has been snapping images of the comet since she drew near a few months ago, which have wowed both scientists and enthusiasts alike. The first close-up looks at the comet revealed its unusual 'rubber duck' shape - something which wasn't apparent from telescope images from Earth - which potentially label the comet as a 'contact binary' (two comet pieces that are so close to one another that they touch, and orbit around each other at the same time). Further images, upon flying closer, have given us more and more detailed looks at the surface features - showing us mountains, cliffs, slopes and valleys, huge craters, and snow, dusty plains strewn with boulders.

Samples of the water and dust already streaming off the comet's surface have given scientists here on Earth plenty to ponder over as well.

RELATED: Rosetta gets a whiff of Comet 67P, and it stinks

What's next?

Both Rosetta and Philae will remain with Comet 67P for at least the next year or so, with the mission set to end sometime in December 2015 (unless it is extended). Philae's survival will depend on the comet's activity, as jets of gas blasting out from the comet as it's warmed by the Sun could bring about an abrupt end to the lander's part of the mission.

During the time that they have, both will examine 67P/Churyumov-Gerasimenko during its relatively quiet period - like it is now, on the 'inbound' part of its orbit - as it becomes more active the closer it gets to the Sun, and then as it quiets down again once the comet heads back out towards the outer solar system.

The purpose of the mission, and the focus of all this concentration onto Comet 67P, is to learn as much as we can about this ancient relic from the formation of our solar system. This will provide us with more information about comets and how they behave, of course, but the composition of the comet may give us clues towards answering some much more important questions. 

One such question is where did Earth get all of its water? Scientists have had ideas about this for quite some time, and comet collisions - early in the planet's history - are a prime suspect.

Another, possibly even more important question, they might answer involves the very origin of live on this planet, as comets may have seeded Earth with complex organic molecules - the very building-blocks of life.

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