Podcaster: Richard Drumm
Title: Space Scoop: Interstellar Snowball Fight Seen for the First Time!
Organization: Astrosphere New Media
Link : astrosphere.org ; http://unawe.org/kids/unawe1443/
Description: Space scoop, news for children.
Bio: Richard Drumm is President of the Charlottesville Astronomical Society and President of 3D – Drumm Digital Design, a video production company with clients such as Kodak, Xerox and GlaxoSmithKline Pharmaceuticals. He was an observer with the UVa Parallax Program at McCormick Observatory in 1981 & 1982. He has found that his greatest passion in life is public outreach astronomy and he pursues it at every opportunity.
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Transcript:
This is 365 Days of Astronomy. Today we bring you a new episode in our Space Scoop series. This show is produced in collaboration with Universe Awareness, a program that strives to inspire every child with our wonderful cosmos.
Today’s story is…
Interstellar Snowball Fight Seen for the First Time!
Occasionally a comet lands in the newspaper headlines when it makes a dazzling light show across our night sky. This maybe gives the impression that comets are rare. However, that’s far from the truth!
In reality, thousands of comets have been discovered in our Solar System and many more are waiting to be found, as Comet Siding Spring showed us with last month’s close pass by Mars. And now we’re finding hundreds of comets around other stars, too! These are called ‘exocomets’.
Like planets, comets orbit their star. Unlike planets they are born in the outer edges of a solar system, far away from the star’s heat and light. They are made out of rocks packed together with ice, mostly water ice, like a dirty snowball.
They are smaller than planets, usually just half a kilometer to a few kilometers in diameter. They don’t emit any light of their own, but reflect the light from their star, so of course they’re very dim in comparison to the star.
As a comet gets closer to its star, the ice begins to sublimate, that is go straight from solid to gaseous, and rises from the surface of the comet like steam rising from a lake. The “steam” forms a cloud or coma around the comet’s head and a tail that can stretch out for as much as 80,000 km! That’s the length of almost eight Earths in a row!
For almost thirty years astronomers have been watching with fascination at the strange, flickering light of a young nearby star called Beta Pictoris. It’s the second brightest star in the constellation Pictor, thus the “Beta” designation. It’s about 63 light years away from our sun, so it’s fairly close as stars go.
Astronomers have long suspected it, but now we know that this strange twinkling effect is caused by hundreds of comets transiting or passing in front of the star!
As they pass in front of the star’s surface- the visible disk of the star, each comet’s solid centre and hazy coma & tail briefly block some small part of the star’s light, making a tiny dip in the light output of the star. Nearly 500 exocomets have already been discovered orbiting this young star!
But that’s not the best part, just wait!
Some French European Southern Observatory astronomers found out (using the HARPS instrument at the La Silla Observatory in Chile) that the comets belong to 2 separate categories! There are old comets, uh exocomets, that have made many passes near their star, and which are apparently in a resonant orbit with the giant planet that orbits the star, a planet called Beta Pictoris B.
In the album artwork that accompanies today’s episode, the planet is seen as a little white dot slightly above & to the left of the center dark spot. That dark spot is where the star is, but it’s light has been largely subtracted from the image, leaving the planet visible.
The orange & red stripes in the album art are the dust disc that surrounds the young star system, imaged here by the ESO’s VLT, the Very Large Telescope also in Chile.
These older comets have weak “signatures” in the light output of the star, so they apparently have small tails which are a result of the comets having sublimated away most of their volatiles such as the water ice from many, many passes close to the star. These comets also have numerous different orbits around Beta Pic, as the star is known.
The other group of comets were apparently younger ones because they caused a larger drop in the star’s light output and thus have large tails. These youngsters are all on nearly identical orbits, which strongly suggests that they probably are a result of a single collision between two of the larger old comets.
Because Beta Pic is such a young star, this cometary activity gives us a glimpse into what the youth of our Sun may well have been like. You know how kids are with snowball fights!
Speaking of cool things, here’s a cool fact:
Around 4,000 comets in a number of different categories have been counted in our Solar System, but its believed that the true number could be more like a trillion! (That’s trillion with a T, a million million!) Holy Moley!
Thank you for listening to 365 Days of Astronomy!
End of podcast:
365 Days of Astronomy
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