快猫短视频

COMET Hale-Bopp has a moon, says a NASA physicist in California. If
confirmed, 鈥淏aby Bopp鈥� would be the first satellite ever discovered for a comet,
and would allow astronomers to measure a comet鈥檚 mass for the first time.

The claims are made by Zdenek Sekanina of NASA鈥檚 Jet Propulsion Laboratory.
Sekanina developed a mathematical model for the brightness of a comet鈥檚 nucleus
and its coma, the cloud of dust and gas that surrounds the nucleus. He then
studied six Hubble Space Telescope digital images of Hale-Bopp鈥檚 core taken
between October 1995 and October 1996, and used his model to strip away the
light from the nucleus and coma.

In five of the six images, a residual bright area emerged, Sekanina found. He
concludes that the bright patch is a satellite about 33 kilometres wide orbiting
about 200 kilometres from Hale-Bopp鈥檚 nucleus. Sekanina thinks observers in
Hawaii and Chile, who recorded a speck of light near Hale-Bopp鈥檚 nucleus on
three occasions between September 1996 and January 1998, also glimpsed the moon.
鈥淚t is perfectly conceivable that this is the same object I was observing,鈥� he
says.

But Harold Weaver, an astrophysicist at Johns Hopkins University who provided
the Hubble images Sekanina analysed, is not convinced. Weaver and his colleague
Philippe Lamy at the Space Research Laboratory in Marseilles, France, strongly
doubt that 鈥淏aby Bopp鈥� is real. 鈥淲e are sceptical, to say the least,鈥� says
Lamy.

Lamy and Weaver believe Sekanina is inferring something from the images that
isn鈥檛 there. 鈥淗e鈥檚 just trying to squeeze too much out of the data,鈥� says
Weaver. He points out that Sekanina analysed the images pixel by pixel, and that
a bright point of light falling on several pixels rather than just one can skew
the results.

Weaver also questions Sekanina鈥檚 model of the comet鈥檚 dusty coma. 鈥淗ale-Bopp
was an extremely dynamic comet, with jets and active regions,鈥� he says. 鈥淎 piece
along a jet can be interpreted as another nucleus.鈥�

Lamy and Weaver also discount the other observations Sekanina cites. Unlike
Hubble images, these ground-based observations required mathematical processing
to minimise atmospheric distortions. Weaver was using the Hubble telescope to
observe Hale-Bopp around the same time. 鈥淚f that double nucleus was really
there, we would have seen it,鈥� he says.

Brian Marsden, a planetary astronomer at the Harvard-Smithsonian Center for
Astrophysics in Cambridge, Massachusetts, is more positive. Many comets have
been known to split up, he says, and a comet as large as Hale-Bopp could, in
theory, keep a fragment in orbit for some time.

Marsden has calculated that 4200 years ago, Hale-Bopp may have passed close
enough to Jupiter to break up, as Comet Shoemaker-Levy 9 did before its
spectacular crash into Jupiter in 1994. 鈥淚 like Sekanina鈥檚 idea, and I tend to
believe it,鈥� says Marsden. 鈥淏ut it鈥檚 not an easy type of observation to make,
and I鈥檓 afraid Sekanina is in the minority.鈥�

In the minority or not, Sekanina is sure of what he saw. 鈥淚f there were one
image, I wouldn鈥檛 believe it at all,鈥� he says. 鈥淲ith two, I鈥檇 still be
sceptical. But I found it on five.鈥� If any new information confirms that the
moon is real, observations of its orbit would reveal Hale-Bopp鈥檚 mass.