ESA's comet-chasing Rosetta spacecraft is nearing the end of its mission. The spacecraft depends on the Sun for power, and had energy to spare when the comet was at perihelion (of about 1.24 AU) on August 13. But the comet has spent the last year rapidly receding from the Sun: it's already nearly at 3.5 AU, beyond the main asteroid belt. So Rosetta's power is declining, with the Sun already 8 times less strong than it was at perihelion. Rosetta survived to great distance from the Sun earlier in its mission only by entering a deep hibernation. ESA isn't going to try that hibernation feat again, and is instead planning to end the mission with a slow spiral into the comet and a controlled impact on September 30.
Last week, ESA announced when and where Rosetta is going to touch down, bringing the mission to an end: within the Ma'at region on the comet's head, at approximately 10:30 UTC (12:30 CEST / 06:30 EDT / 03:30 PDT) on September 30. It took me a while to figure out its position relative to the Philae landing locations -- comet geography is challenging! -- but I think this is how they all relate to each other:
Base map: ESA / Rosetta / MPS for OSIRIS Team MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA. Landing site locations: Emily Lakdawalla.
Map of comet Churyumov-Gerasimenko regions with landing locations
The 19 regions identified on Comet 67P/Churyumov–Gerasimenko are separated by distinct geomorphological boundaries. Following the ancient Egyptian theme of the Rosetta mission, they are named for Egyptian deities. They are grouped according to the type of terrain dominant within each region. Five basic categories of terrain type have been determined: dust-covered (Ma’at, Ash and Babi); brittle materials with pits and circular structures (Seth); large-scale depressions (Hatmehit, Nut and Aten); smooth terrains (Hapi, Imhotep and Anubis), and exposed, more consolidated (‘rock-like’) surfaces (Maftet, Bastet, Serqet, Hathor, Anuket, Khepry, Aker, Atum and Apis). All three landing sites (Philae initial and final sites and the planned resting place of the Rosetta orbiter) are located on the northern part of the "head" of the comet.
Rosetta's increasing distance from the Sun means that it no longer has enough power to run all of its subsystems, and the mission has begun to turn off nonessential ones. That has brought Rosetta to a symbolic and sad moment: tomorrow at 09:00 UTC, they will shut down the Electrical Support System Processor Unit, a piece of equipment that is nonessential because it used to be used to communicate with the now-silent Philae. We knew already that Philae would likely never be heard from again after its last contact in July 2015, but the shutdown of this piece of equipment makes that absolutely final.
It's sad to say goodbye to Philae; it'll be much sadder to say goodbye to the scientifically productive mothership, Rosetta. But the final phase of the mission will be thrilling as it brings us ever-closer views of the comet!
ESA / Rosetta / MPS for OSIRIS Team MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA
Closeup on a comet's fracture
Rosetta took this photo of comet Churyumov-Gerasimenko on July 20, 2016 from a distance of about 9 kilometers. At full size it has a resolution of 16 centimeters per pixel. At lower right are highly fractured yet still coherent blocks. Running across the left side of the image is a fracture that appears to be opening, allowing fine-grained surface material to collapse into the fissure.
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