When will Comet Elenin come
closest to the Earth and appear the brightest?
Comet Elenin should be at its brightest shortly before the time
of its closest approach to Earth on Oct. 16, 2011. At its
closest point, it will be 22 million miles (35 million
kilometers) from us.
Will Comet Elenin come close to the Earth or between the
Earth and the moon?
Comet Elenin will not come closer to Earth than 22 million miles
(35 million kilometers). That's more than 90 times the distance
to the moon.
Can this comet influence us from where it is, or where it
will be in the future? Can this celestial object cause shifting
of the tides or even tectonic plates here on Earth?
There have been incorrect speculations on the Internet that
alignments of comet Elenin with other celestial bodies could
cause consequences for Earth and external forces could cause
comet Elenin to come closer.
"Any approximate alignments of
comet Elenin with other celestial bodies are meaningless, and
the comet will not encounter any dark bodies that could perturb
its orbit, nor will it influence us in any way here on Earth,"
said Don Yeomans, a scientist at NASA JPL.
"Comet Elenin will not only be far away, it is also on the small
side for comets," said Yeomans. "And comets are not the most
densely-packed objects out there. They usually have the density
of something akin to loosely packed icy dirt.
"So you've got a modest-sized icy dirtball that is getting no
closer than 35 million kilometers [about 22 million miles),"
said Yeomans.
"It will have an immeasurably minuscule influence
on our planet. By comparison, my subcompact automobile exerts a
greater influence on the ocean's tides than comet Elenin ever
will."
I've heard about three days of darkness because of Comet
Elenin. Will Elenin block out the sun for three days?
"As seen from the Earth, comet Elenin will not cross the sun's
face," says Yeomans.
But even if it could cross the sun, which it can't,
astrobiologist David Morrison notes that comet Elenin is about
2-3 miles (3-5 kilometers) wide, while the sun is roughly
865,000 miles (1,392,082 kilometers) across.
How could such a
small object block the sun, which is such a large object?
Let's think about an eclipse of the sun, which happens when the
moon appears between the Earth and the sun. The moon is about
2,500 miles (4,000 kilometers) in diameter, and has the same
apparent size as the sun when it is about 250,000 miles (400,000
kilometers) away -- roughly 100 times its own diameter.
For a
comet with a diameter of about 2-3 miles (3-5 kilometers) to
cover the sun it would have to be within 250 miles (400
kilometers), roughly the orbital altitude of the International
Space Station.
However, as stated above, this comet will come no
closer to Earth than 22 million miles.
I've heard there is a "brown dwarf" theory about Comet Elenin.
Would its mass be enough to pull Comet Honda's trajectory a
significant amount? Could this be used to determine the mass of
Elenin?
Morrison says that there is no 'brown dwarf theory' of this
comet.
"A comet is nothing like a brown dwarf. You are correct
that the way astronomers measure the mass of one object is by
its gravitational effect on another, but comets are far too
small to have a measureable influence on anything."
If we had a black or brown dwarf in our outer solar system, I
guess no one could see it, right?
"No, that's not correct," says Morrison.
"If we had a
brown
dwarf star in the outer solar system, we could see it, detect
its infrared energy and measure its perturbing effect on other
objects. There is no brown dwarf in the solar system, otherwise
we would have detected it. And there is no such thing as a black
dwarf."
Will Comet Elenin be visible to the naked eye when it's
closer to us? I missed Hale-Bopp's passing, so I want to know if
we'll actually be able to see something in the sky when Elenin
passes.
We don't know yet if Comet Elenin will be visible to the
naked eye.
Morrison says,
"At the rate it is going, seeing the
comet at its best in early October will require binoculars and a
very dark sky. Unfortunately, Elenin is no substitute for seeing
comet Hale-Bopp, which was the brightest comet of the past
several decades."
"This comet may not put on a great show. Just as certainly, it
will not cause any disruptions here on Earth. But, there is a
cause to marvel," said Yeomans.
"This intrepid little traveler
will offer astronomers a chance to study a relatively young
comet that came here from well beyond our solar system's
planetary region. After a short while, it will be headed back
out again, and we will not see or hear from Elenin for thousands
of years. That's pretty cool."
This comet has been called 'wimpy' by NASA scientists. Why?
"We're talking about how a comet looks as it safely flies past
us," said Yeomans of NASA's Near-Earth Object Program Office.
"Some cometary visitors arriving from beyond the planetary
region - like
Hale-Bopp in 1997 - have really lit up the night
sky where you can see them easily with the naked eye as they
safely transit the inner-solar system.
But Elenin is trending
toward the other end of the spectrum. You'll probably need a
good pair of binoculars, clear skies and a dark, secluded
location to see it even on its brightest night."
Why aren't you talking more about Comet Elenin? If these
things are small and nothing to worry about, why has there been
no public info on Comet Elenin?
Comet Elenin hasn't received much press precisely because it is
small and faint. Several new comets are discovered each year,
and you don't normally hear about them either.
The truth is that Elenin has received much more attention than it deserves due to
a variety of Internet postings that are untrue. The information
NASA has on Elenin is
readily available on the Internet. If this
comet were any danger to anyone, you would certainly know about
it.
For more information, visit NASA's
AsteroidWatch site.
I've heard NASA has observed Elenin many times more than
other comets. Is this true, and is NASA playing this comet down?
NASA regularly detects, tracks and characterizes asteroids and
comets passing relatively close to Earth using both ground- and
space-based telescopes.
The Near-Earth Object Observations
Program, commonly called "Spaceguard," discovers these
objects, characterizes a subset of them and predicts their paths
to determine if any could be potentially hazardous to our
planet. For more information, visit the
NASA-JPL Near Earth objects site.
However, neither NASA nor JPL is in the business of actively
observing Elenin or any other comet. Most of the posted
observations are made by amateur astronomers around the world.
Since Elenin has had so much publicity, it naturally has
attracted more observers.
I was looking at the orbital diagram of Comet Elenin on the
JPL website, and I was wondering why the orbit shows some angles
when zooming? If you pick any other comet, you can see that
there are no angles or bends.
Many people are trying to plot the orbit of the comet with the
routine on the JPL website, without realizing that this is just
a simple visualization tool.
While the tool has been recently
improved to show smoother trajectories near the sun, it is not a
scientific program to generate an accurate orbit. Yeomans
explains that the orbit plotter on the Near-Earth Object website
is not meant to accurately depict the true motion of objects
over long time intervals, nor is it accurate during close
planetary encounters.
For more accurate long-term plotting, Yeomans suggests
using the JPL Horizons system instead.
