Podcaster: Richard Drumm
Title: Space Scoop: When the Planet Team Lost a Player
Organization:365 Days Of Astronomy
Link : astrosphere.org ; http://unawe.org/kids/unawe1134/
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: When the Planet Team Lost a Player
What is a planet? This sounds like it should have a simple answer, but only a few years ago this question was giving astronomers a headache!
When they finally came up with an answer it had big consequences: The number of planets in our Solar System went from nine back to eight!
The planet that was kicked out of the club is Pluto.
This was the most distant planet from the Sun and by far the smallest in our Solar System. Pluto is actually smaller than our Moon. So small that many astronomers argued that it wasn’t actually a planet.
Instead, they said it belonged to the group of small Kuiper Belt objects that were being discovered in the outer parts of the Solar System beyond Neptune.
Then, in 2003, Caltech astronomer Dr. Mike Brown found an object in the outer Solar System, originally called 2003 UB313 and now called Eris, which they thought could be bigger than Pluto. Eris is 96 times farther away from the Sun than Earth is, and about 3 times farther away from the Sun as Pluto, so observing it is challenging.
From this discovery and with the certainty that more objects like it would be found, Pluto’s fate was decided by the IAU, the International Astronomical Union: it would no longer be called a planet.
Instead, astronomers created the new title ‘dwarf planet’ for Pluto, Eris and other similar objects. In a way Pluto had been demoted!
However, in 2010 astronomers were able to measure the size of the dwarf planet Eris more accurately and they have discovered that it isn’t bigger than Pluto after all – they’re actually about the same size.
Eris’s newly determined diameter stands at 2,326 ±12km. Because of the New Horizons spacecraft’s fly-by of Pluto, it’s is now known to be 2,374 ±8km in diameter, or about 48km bigger.
So how the heck do we know Eris’s size so accurately?
It was an occultation timing event that provided the information. An occultation is where a planet or the Moon passes in front of a background star and in effect the shadow of the planet passes over the Earth.
In occultation timing astronomy a number of telescopes are arrayed across the path of the “shadow” and a record of the exact time where the star disappears and reappears is noted. At first the light we see is the sum of both the planet and the star, then it’s just the light from the planet, then it’s both objects again.
By positioning telescopes across the shadow’s path it’s possible to make a precise determination of the size & shape of the shadow. The more telescopes, the better the graphic represents the shape of the shadow and therefore, of course, the shape of the planet.
By a lucky chance in November of 2010, Eris passed in front of a faint 17th magnitude star in the constellation Cetus, the whale, as seen from Earth. Eris itself is even fainter at magnitude 18.7.
Brazililan astronomer Dr. Marcelo Assafin of the Observatório do Valongo predicted the occultation in 2009, but there was uncertainty about where on Earth the shadow of Eris would pass.
It could be anywhere from Alaska to central Chile.
On November 4th, only 2 days before the occultation, Eris’s orbit was refined more and the position of the star was refined more and it was discovered that the occultation would occur over Chile, Peru, Bolivia and Brazil.
So French astronomer Dr. Bruno Sicardy of the Observatoire de Paris-Meudon sent word out to observatories and amateur astronomers to observe the event. Teams set up at 26 locations to view the event.
Only 2 succeeded. A third observed but missed the shadow. You can see a graphical representation of the shadow of Eris and the data that astronomers gathered in today’s album artwork.
You can see 2 chords or lines that are interrupted by the shadow of Eris. Since we know how far apart those 2 observatories are we can measure the diameter of the circle that best fits the observations and measure the diameter of Eris.
We can safely assume that Eris is spherical as all bodies of that size do have enough gravity to compress themselves to the smallest size, which is a sphere.
The first telescope that successfully made an observation of the event was the 24″ TRAPPIST Ritchey–Chrétien telescope at the La Silla Observatory in Chile. TRAPPIST stands for TRAnsiting Planets and PlanetesImals Small Telescope. Dr. Emmanuël Jehin was operating the telescope in La Silla.
This telescope is dedicated to studying transiting exoplanets around distant stars and comets orbiting around our Sun. The name highlights the Belgian origins of the project. The Belgian Trappist monks brew some of the finest beers and ales in the world.
The second telescope that successfully observed the occultation was Canadian amateur astronomer Caisey Harlingten’s 20″ Planewave Dall-Kirkham telescope at San Pedro de Atacama in northern Chile.
That team was led by Alain Maury, a much celebrated French former professional astronomer, discoverer of 7 asteroids and 2 comets, who is currently an independent observer.
Two telescopes at that location observed the event, but the Harlingten telescope was equipped with a significantly better camera and got much better data. The occultation lasted 76 seconds for them.
The Brazilian team was clouded out.
This was just enough observations to ascertain Eris’s size. More observations would have narrowed the error bars a bit, but at least we got these 2 timings! Larger telescopes would have helped determine if Eris has an atmosphere, but we got the data we needed.
Eris will occult other stars in the future and maybe we can enlist the help of larger observatories then. This event does underscore the usefulness of smaller observatories.
Who knows, maybe if astronomers had known the true size of Eris back in 2005, Pluto might have stood a better chance of staying on the planet team.
But don’t worry about Pluto. It doesn’t care what we call it. It has now had it’s portrait taken and lots of good science data gathered by the New Horizons spacecraft. Now we can proudly call it the King of the Kuiper Belt!
And when Pluto became a dwarf planet, the largest asteroid in the asteroid belt, Ceres, was upgraded to the category of dwarf planet as well. Ceres now has the NASA Dawn spacecraft orbiting it bringing us gigabytes of new information about small solar system objects!
Hey Here’s a Cool Fact!
Don’t worry abut Eris either! Because it has a moon, Dysnomia, we are able to determine how much mass Eris has. It’s 27% more massive than Pluto, so it’s got to have a rocky core and a thin covering of ice.
Eris is the second brightest object in the solar system in terms of its reflectivity or albedo. It’s second only to Saturn’s moon Enceladus. The dwarf planet probably had an atmosphere which has frozen out onto the surface making it whiter than new fallen snow.
In a couple hundred years, when Eris gets closer to it’s perihelion at about 40 AU from the Sun, the frost will likely sublimate back into a thin atmosphere again and Eris will look even more like Pluto!
Thank you for listening to the 365 Days of Astronomy Podcast!
End of podcast:
365 Days of Astronomy
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