Australian Sky & Telescope — July 2017

http://www.skyandtelescope.com.au 29

PLOT: KATHRIN ALTWEGG ET AL. /

SCIENCE

; IMAGES: ESA / ROSETTA / MPS FOR OSIRIS TEAM (3)

building blocks that created comets and eventually planets?

Results from Philae

In addition to the CONSERT measurements of the interior of

thenucleus,Philaeprovidedvaluablemeasurementsaboutthe

properties of the comet’s surface. Even the unplanned ‘bounces’

helped us gauge the hardness of the surface. Thanks to MUPUS,

which tried to hammer an instrumented penetrator into the

nucleus, we know that there’s a surface layer of dust covering a

veryhard,compacteddust-icecrust.Thelanderalsoconfirmed

that the nucleus has no intrinsic magnetic field.

COSAC,whichpairedagaschromatographandmass

spectrometer, identified 16 organic compounds, four of

which — including acetone and acetamide — had never been

detectedinacomet.GasesmeasuredbyPtolemy,anothermass

spectrometer,containednotonlytheexpectedwater,carbon

monoxide and carbon dioxide, but also organic compounds

including formaldehyde. Many of these compounds are

important in creating amino acids, sugars, and nucleobases.

In addition, ROSINA detected the amino acid glycine. Even if

comets didn’t supply the majority of water on Earth, they could

have provided essential raw materials for life.

We’ll never hear from Rosetta again, but this is not the

last that we’ll hear from its host. The comet will have a

fairly close encounter with Jupiter, only about 56 million

kilometres, at its next aphelion in November 2018. Jupiter’s

gravitational tweak will decrease 67P’s perihelion. So when

the comet next comes its closest to the Sun, on November 2,

2021, chances are good that we’ll see more vigorous activity.

That coming apparition also offers quite good observing

geometry from Earth, with the comet just 0.42 astronomical

unit (63 million km) away and well positioned high in the

northern night sky (declination +26°).

But it will be a long time, if ever, that we’ll see Comet 67P/

Churyumov-Gerasimenko as well as we have these past three

years. And as I watched Rosetta take its final plunge to the

surface, streaming to us in real time images of new vistas

seen in more detail than ever before, I couldn’t help but think

of this quote from the movie Blade Runner:

“I’ve seen things you people wouldn’t believe. Attack ships on

fire off the shoulder of Orion. I watched C-beams glitter in

the dark near the Tannhauser Gate. All those moments will

be lost in time, like tears in rain. Time to die.”

Rest in peace, Rosetta and Philae. I’m sure those moments

will not be lost as we continue to use this mission’s vast

stockpile of data to further our knowledge about comets, the

origin of our Solar System, and perhaps ourselves.

„JOEL PARKER (Southwest Research Institute) is on the

science teams of Rosetta and several other space missions. He

produces and hosts the radio science show “How on Earth”.

ICY FIREWORKS On July 29, 2015, just

two weeks before reaching perihelion,

the comet unleashed an intense but

short outburst of gas and dust. These

three images span just 36 minutes.

SWATER’S ORIGINSThe proportions of hydrogen and its heavier

isotope deuterium vary widely across the Solar System. The ratio is

unexpectedly high in Rosetta’s comet, 67P/Churyumov-Gerasimenko,

implying that most of Earth’s water must have come from water-rich

asteroids or was already here when our planet formed.

Protosolar nebula

Outer planets Oort Cloud comets

Jupiter-family

comets

Deuterium-to-hydrogen ratio (D:H)

10 –5

10 –4

10 –3

Jupiter

Saturn

Uranus

Enceladus

Asteroids

C/1995 O1 (Hale-Bopp)

C/2001 Q4 (NEAT)

C/2009 P1 (Garradd)

C/1996 B2 (Hyakutake)

C/2002 T7 (LINEAR)

8P/Tuttle1P/Halley

45P/H-M-P

103P/Hartley 2

67P/C-G

153P/Ikeya-Zhang

Earth

Neptune