[meteorite-list] Naked-Eye Comet Possible for Christmas 2001

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:41:12 2004
Message-ID: <200102261810.KAA19470_at_zagami.jpl.nasa.gov>

http://www.space.com/scienceastronomy/solarsystem/xmas_comet_010223.html

Naked-Eye Comet Possible for Christmas 2001
By Robert Roy Britt
space.com
26 February 2001

A comet detected three months ago is ambling toward the inner solar system
and could be visible to the naked eye late this year, possibly providing the
best comet show since Hale-Bopp in 1997. Tickets to the show should be
popular, as the comet threatens to make its apparition a one-time
engagement.

The comet was first thought to be an asteroid when it was spotted Nov. 16,
2000 by researchers at the Lincoln Laboratory Near-Earth Asteroid Research
project (LINEAR). It was later identified as a comet and given the official
designation of 2000 WM1. Scientists are referring to it as Comet LINEAR, but
it is different from the comet 1999 S4, also called Comet LINEAR, which
broke apart late in the summer of 2000.

"Although no comet can be relied upon completely, there is a very good
chance that [this comet] will be a naked-eye Christmas comet for 2001," says
astronomer Mark Kidger.

The show is expected to continue into early 2002.

How bright will it be?

Comets are made mostly of dust and gas, primarily carbon dioxide, ammonia
and methane. Scientists liken them to dirty snowballs. Predicting how bright
they will get as they approach the inner solar system has proven tricky in
the past.

Like all comets, 2000 WM1 will loop around the Sun, though its path is not
yet known with certainty. As it approaches the Sun, gas and dust will burn
off of at an increasing rate. Sunlight reflecting from this material will
make the comet's head, or coma, grow brighter. The gas and dust will be
pushed away by charged particles known as the solar wind, forming two tails.
Dust particles form a yellowish tail, and ionized gas makes a bluish ion
tail. The tails always point away from the Sun.

How bright a comet gets depends on many factors, including its size, exactly
what it's made of and how close it gets to the Sun and Earth.

Estimates by Brian Marsden at the International Astronomical Union's Minor
Planet Center put the peak brightness for Comet LINEAR at roughly magnitude
4. On this scale, higher numbers are fainter. The faintest object visible to
the naked eye under dark rural skies is about magnitude 6, for example. The
brightest stars are around magnitude minus 1.4. Venus, at its most
brilliant, reaches minus 4.4.

Kidger figures the peak brightness will be between magnitude 3 and 5,
sometime in November, and he's optimistic that it will be on the brighter
side. Better estimates will be possible in April or May, he says.

"In all cases apart from the most pessimistic, the comet should be naked-eye
visible," Kidger says. "The worst case would make it an easy binocular
object."

NASA's Ron Baalke echoed Kidger's caution, saying that predicting the
brightness of a comet is far from an exact science. "The current estimates
on how bright the comet may be varies from magnitude 3 to magnitude 7,"
Baalke said. "There is a possibility the comet may be a naked-eye comet, but
there is no guarantee that it will be."

As of Feb. 21, Comet LINEAR was 447 million miles (719 million kilometers)
from the Sun, about as far out as Jupiter, and poking along at 42,500 miles
per hour (19 kilometers per second). The Sun's gravity has pulled the comet
in from the distant Oort Cloud, a reservoir of icy bodies that surrounds the
solar system and was created back when the Sun formed, some 4.5 billion
years ago.

As the dirty snowball gets closer to the Sun, it will speed up enormously,
Kidger explains, reaching a top speed of 125,300 miles per hour (56
kilometers per second) on Jan. 22, 2002. On that day, it will be at its
closest point to the Sun, some 51.7 million miles (83.2 million kilometers)
away. Scientists call this perihelion.

Astronomers suspect that 2000 WM1 is a "new" comet, making its first pass
from the Oort Cloud into the inner solar system. Marsden of the minor planet
center calculates that it won't come around again for at least 100,000
years. However, the orbit appears to be "open," meaning that 2000 WM1 may
shoot off into interstellar space and never return.

Similar to Hyakutake

Kidger says the comet's diameter is roughly 2 miles (3 kilometers), though
this estimate may change as better observations are made. On approach to the
Sun, the comet will pass within 30 million miles (49 million kilometers) of
Earth in early December.

This scenario will be similar to Comet Hyakutake in 1996, which was
estimated to be about the same size and came within 9.3 million miles (15
million kilometers) of our planet. Comet Hale-Bopp in 1997 was much larger,
some 25 to 44 miles (40 to 70 kilometers) wide. But Hale-Bopp was almost 15
times farther away than Hyakutake. Both comets made for delightful naked-eye
viewing and fabulous telescopic photographs.

Like Hyakutake, Comet LINEAR may reach its peak brightness before
perihelion. Kidger says this means that while it should be easy to see, the
comet's tail may not be very spectacular.

"The fact that the comet is new suggests that it will probably brighten
quickly initially and then slow down considerably as it gets closer to the
Sun and the fresh ices on the surface of the nucleus are exhausted," Kidger
says. "A consequence of this is that it is unlikely that the comet will have
a bright tail when [it is] closest to the Earth and brightest at the end of
the year. Even though Comet LINEAR may be quite bright and easy to see with
the naked eye, it may be little more than a fuzzy patch in the sky."
Received on Mon 26 Feb 2001 01:10:42 PM PST