Do you remember this eager little guy who was nicknamed "leek" by Chinese netizens?
Today, 721 days after landing on the comet, at 17:00 Beijing time, the Rosetta probe shut down the only means of communication with the Philae lander.
It's time to say goodbye... Image source: Twitter
【Our Rosetta】
Rosetta has spent 12 years in the harshness of space, two of which have been spent on the edge of dusty comets, and its lifespan has come to an end. As the comet returns to the icy space of Jupiter's orbit, less and less sunlight can be used, and the bandwidth that can be used to transmit scientific data is getting narrower and narrower.
In 2011, while Rosetta and Philae were still on the road, it entered a 31-month dormancy at the far end of the orbit. Five years later, it was once again in the darkness far from the sun — but this time, with Comet 67p. At aeronautics, the distance between 67p and the Sun reached 850 million kilometers, and Rosetta had never been so far away, nor had it stayed here for so long; its heating device would not be enough to guarantee its survival in this bitter winter.
So ESA decided that, instead of going gently into that good night, it would be better to let the short life burn one last time: Rosetta would follow in Philae's footsteps and land on the comet together.
Comet 67p/Chulyumov-Gracimenko, which we call Rosetta's Comet, will also be her final resting place.
This means that in order to reserve energy for the final landing, all components that are no longer necessary must be shut down early – including the electronic support system processing unit (ess), the only communication window for Philae.
Closing this window, they say, is the final goodbye to Philae. They said that even if Philae woke up again and signaled again, no one would ever hear again. But we all know that this wouldn't have happened. Even last summer, when it was closest to the sun, it transmitted only a few brief signals intermittently; as 67p moved away, researchers already knew it wouldn't wake up again.
【Our Philae】
Philae landed on Comet 67p on November 12, 2014. This was the first attempt by humans to use a harpoon fixture in space, but the attempt was unsuccessful: instead of fixing itself to the intended landing site, Philae bounced four times and fell into the shadow of a cliff a kilometer away, and the solar panels could not get enough energy. After 64 hours of operation, its backup battery finally ran out and went into sleep mode — in that short time, Philae completed 80 percent of its scheduled detection projects.
On November 12, 2014, Philae landed on Comet 67p and bounced, a series of photos taken by Rosetta documented the process. Image credit: esa/rosetta/mps for osiris team mps/upd/lam/iaa/sso/inta/upm/dasp/ida
On November 15, the "Philae", which did not get enough sunlight, ran out of power and entered deep sleep mode. Contact was briefly restored until June. (The medals on the cliff were the first, second, third, and fourth probes that successfully landed on the comet: Philae bounced three times on the surface of the comet before settling.) Image credit: esa
But at that time, Comet 67p was still on its way to the Sun. The researchers know that the comet will reach perihelion on August 13, 2015, and perhaps the sunlight here will be enough to wake Philae. According to preliminary calculations, by the end of March 2015, sunlight may be able to warm Philae to minus 45 degrees Celsius – its operating temperature limit.
However, it wasn't until June 13, 2015, that Rosetta finally received Philae's signal. The analysis shows that Philae actually woke up on April 26, but has not been able to establish contacts. Engineers worry that this means its signal transmission device may have been damaged. For the weeks that followed, Philae's signal remained weak and incoherent; after July 9, it fell into a persistent silence. Although the temperature is still rising, even reaching 0 degrees Celsius in August, people have never waited for the sound of it again.
On June 14, the Comet Philae, which had been sleeping for nearly seven months, woke up and made brief contact with scientists on the ground. Then came a year-long silence.
After the last communication disappeared, Rosetta waited for a whole year. No waiting is forever, today is the day of farewell —
However, in 65 days, Rosetta will land at 67p. The landing process will allow Rosetta to probe and collect data with unprecedented precision; but it will also mean that once it lands, Rosetta will no longer have any remaining energy, its communication will be shut down, and all operations will end.
All goodbyes will end with a reunion.
To release Philae, Rosetta made orbital changes during its orbit around 67p. Today, rosetta is also about to land on 67p, and it will be in the dark at the same time. Image source: esa
【Our 67p】
Comet 67p was born in the Kuiper Belt, where ice balls are a relic of the early days of the solar system. The researchers speculate that some of these objects collided with Earth as comets, providing a vital source of water for early Earth life, and possibly even the first organic molecules. If that's the case, then we and everything we create today have contributed to these comets.
The remaining objects — including Comet 67p — drift down the solar system. Most stay in the distant darkness, and a few periodically enter the inner circle of the solar system due to gravitational perturbations, and Comet 1p/Halley may be one such member. For 4.6 billion years, they have not had any contact with other celestial bodies except for accidental impacts.
But in the last 721 days, descendants of one comet have visited another.
This is the photo sent back after the Philae landing, and it is also the first photo taken by humans from the surface of a comet. "Philae" worked here for 64 hours before going to sleep due to running out of batteries. Image source: esa
Over the past 721 days, Rosetta and Philae have taken the sharpest ever photograph of the 67p, probing its structure and chemical composition and glimpsed the moment when the solar system was born 4.6 billion years ago. Over the next 65 days, Rosetta will gradually land toward 67p to complete the final probe; then they will remain on the surface of 67p and rotate around the sun together.
It takes 2355.68 days for 67p to circle the sun, and when it returns next time, it will be greeted only by silence. But we will still be able to see its tail glow– a light that comes from the eternal illumination of the sun, from the volatilization of the comet's ancient molecules, and now there will be atoms from human civilization involved.
You won't be alone again. You will never be alone.
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