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Rings around an asteroid

by Tanya
Publish date
31 March 2014
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In a surprise discovery, two rings have been found around the asteroid Chariklo, making it the first small Solar System body known to have rings.

Saturn is known for its magnificent rings and the other gas giants - Jupiter, Uranus and Neptune - have ring systems too, though not quite as impressive. Careful searches had not found any other ring systems within the Solar System and many astronomers were beginning to think that rings might only exist around large objects, until now.

Rings from Chariklo An artist's impression of the newly discovered rings around Chariklo.
Source: ESO/L. Calçada/Nick Risinger (

Chariklo is just 250km across and lies beyond Saturn, at a billion kilometres away. It is much too small and far away for the rings themselves to be seen, but amazing detail is now known about them. The rings are dense but narrow, just three and seven kilometres wide, and are separated by a clear gap of nine kilometres. If you were standing on the surface of Chariklo, the rings would appear as wide as our Full Moon and stretch from horizon to horizon.

The discovery was made possible because last June, Chariklo passed in front of an obscure star (UCAC4 248-108672). Not only did Chariklo block the star's light for 5 seconds, but two tiny dips in the starlight were seen, just before and after Chariklo moved by. This video from the European Southern Observatory (ESO) shows faint dimming caused by the rings, just before and after Chariklo blocks the star completely.


This event, known as an occultation, could only be seen from South America and an observing campaign was coordinated across seven observatories, including two telescopes operated by the ESO at La Silla, Chile. Having observations from all seven observatories, ruled out other possible explanations, except for a ring system.

What I really love is the data from the new high-resolution camera on ESO's 1.54m Danish telescope. (Anyone who has been to my Discover the Night Sky series knows that I am particularly fond of beautiful graphs!) This new camera was developed to search for exoplanets and can take up to 40 images per second. It was actually able to see the gap between the two rings – now that's beautiful science!

Chariklo Data The data captured by ESO's 1.54m Danish telescope, showing Chariklo blocking out the light of the star (the main dip). On either side are two small, double dips, as the rings also passed in front of the star.
Image: F. Braga-Ribas et al.
Source: Reprinted by permission from Macmillan Publishers Ltd: Nature (March, 2014)

The Planetarium's astronomer, Dr Tanya Hill, was recently appointed the Australian representative of the European Southern Observatory's Science Outreach Network.


Asteroid zooms by Earth

by Tanya
Publish date
11 February 2013
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Most of the time we rush through space without giving it a second thought. But every now and again the Universe reminds us that we are not alone.

On Saturday morning, 16 February, Earth will be buzzed by asteroid ‘2012 DA14’. Its closest approach at 6:25am, will bring it 34,000km from Earth. That’s just a little closer than the geosynchronous satellites – a ring of communication and weather satellites that orbit the Earth at 36,000km. Earlier predictions had the asteroid coming even closer, but Earth’s gravity keeps tugging on the asteroid and changing its predicted path, ever so slightly.

Flight path of asteroid 2012 DA14 The path of asteroid 2012 DA14, which approaches Earth from "below" and passes through the ring of geosychronous satellites. The times given are AEDT.
Source: NASA/JPL-Caltech

One thing is quite clear – there is no chance the asteroid will collide with Earth and that’s a good thing. At 45 metres across, it’s not particularly small and probably of similar size to the asteroid that exploded over Siberia in 1908. Known as the Tunguska event, it flattened 80 million trees across an area the size of Port Phillip Bay.

Path of asteroid 2012 DA14 from Melbourne The path of asteroid 2012 DA14 across the south-west sky as seen from Melbourne on the morning of Saturday 16 February 2013. The times indicated are in AEDT while the positions with relation to the horizon are calculated for 5:25am.
Source: Melbourne Planetarium

Asteroid 2012 DA14 won’t be bright enough for us to see, but experienced observers could catch a glimpse with a small telescope. It will appear in the south-west, just below the Southern Cross – the hard thing will be pin-pointing it while it’s zipping along at 28,000 km/hour.

The rock was discovered almost a year ago by the La Sagra Observatory in southern Spain. It’s one of a handful of observatories that hunt and monitor Near Earth Objects. Each day, about a hundred tons of interplanetary material falls onto Earth – mostly dust from comets or small fragments from asteroid collisions. But once every 100 years, we expect something larger, like 2012 DA14, to appear. It’s nice to know there are people out there looking and making sure our path is clear.

Trees felled by the Tunguska explosion. The Tunguska event was caused by a similar sized asteroid exploding over Siberia in 1908.
Source: the Leonid Kulik Expedition


A Ustream feed of the flyby from a telescope at NASA's Marshall Space Flight Center in Alabama, will be broadcast from 1pm to 4pm, 16 February (AEDT).

Animations and interviews by NASA scientists

Accounts of the Tunguska event from Science at NASA

Asteroid flyby

by Tanya
Publish date
7 November 2011
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On Wednesday 9 November an asteroid is going to fly past Earth.

Vesta from Dawn spacecraft NASA's Dawn spacecraft was sent to the Asteroid Belt to obtain close-up images of Vesta.
Source: NASA

But not this one! This is a picture of Vesta, the third largest asteroid in the Asteroid Belt, located about 200 million kilometres away. This lovely picture was taken by the Dawn spacecraft, which is currently in orbit around Vesta. It shows what a large asteroid looks like from a distance of just 5,200km.


asteroid 2005 YU55
Radar image of the near-Earth asteroid 2005 YU55 when it was 2.4 million km away.
Source: NASA/Cornell/Arecibo

The asteroid that is going to fly past Earth is known as 2005 YU55. This radar image of the asteroid was made last year using the Arecibo Radar Telescope in Puerto Rico. At 400m across this near-Earth asteroid is over 1,000 times smaller than Vesta. Rather than having to send a spacecraft out to it, this asteroid is coming to us.

But there’s no need to go crazy - the closest the asteroid will get is 325,000 km from Earth. That’s just a little closer than the Moon which on average is 380,000 km away. It won’t pose any threat to Earth or have any noticeable gravitational effect. But we should get a great look at it.

NASA scientists will be using antennae from the Deep Space Network to bounce radio waves off the space rock. The data is then used to create a three-dimensional model of the asteroid and with the asteroid being so close it should provide us with a really detailed image so we can learn more about it.

Hundreds of asteroids have been observed using radar astronomy and the interesting thing is that asteroids can be so different. They come in all sorts of shapes and sizes, with some having very smooth surfaces and others being rough and textured. Radar astronomy can also be used to determine the composition of an asteroid and it's even discovered some asteroid moons.

Most importantly of all, radar astronomy gives us the best insight into an asteroid’s trajectory. That’s how we can work out that this near-Earth asteroid won’t harm us and provides the lead time to prepare for great science observations like this one.

I look forward to the day when astronauts will once again take the leap beyond Earth orbit. Many say that after the Moon, the next step for astronauts should be a near-Earth asteroid. The information that’s gathered now could one day be used to choose just which asteroid we'll be visiting.


JPL’s Asteroid Watch Page

NASA’s Near Earth Object Program

Vesta, the brightest asteroid

by Tanya
Publish date
29 July 2011
Comments (1)

Now is your chance to see an asteroid from within the asteroid belt. Vesta will be at its best for the next few weeks and it is the only asteroid that can ever be seen with the naked eye. Even thought it's smaller and further away than the dwarf planet Ceres (the largest object in the asteroid belt), Vesta's surface is great at reflecting sunlight.

Mind you, it still won't be easy. Astronomers measure brightness in magnitudes and by historic convention, the lower the magnitude, the brighter the object. The Sun comes in at a whopping -27. Alpha Centauri, a famous bright star and the closest star to the Sun, clocks in at -0.3.

In comparison Vesta, at its brightest, will reach a magnitude of 5.6. That's only just above the naked eye limit. So you will have to get out to a dark location to see it. Of course with binoculars or a small telescope you'll be doing much better. Remember though, it's only 530km across, so it will only ever look star-like.

Finding chart for Vesta at 9pm on 5th August.Finding chart for Vesta looking eastward at 9pm on 5th August, prepared with the help of "Starry Night" software.
Source: Museum Victoria

So what's so special about now? Vesta will be at opposition on the 5th August, which means opposite the Sun in the sky. It will be in the sky all night and all of the Sun's light will be shining on it (just like a Full Moon occurs when the Moon is at opposition).

And there's more - objects are generally closer to us at opposition and this opposition will bring the asteroid particularly close - still 184 million km away, but 27 million km closer than last year.

NASA's Dawn Spacecraft was 5,200km from Vesta when it took this image.NASA's Dawn Spacecraft was 5,200km from Vesta when it took this image.

But for a really close view of Vesta, nothing can beat the Dawn Spacecraft which entered orbit around the asteroid just two weeks ago. Dawn is the first craft to orbit an asteroid and will stay with Vesta for a year before moving on to study Ceres.

Exploring Vesta is sure to uncover some fascinating science. Asteroids are the oldest objects in the Solar System and from them we hope to learn more about how the planets, including Earth, formed.

And did you know that we have more pieces of Vesta here on Earth, than we have of the Moon! It's clear that something crashed into Vesta creating a huge crater and all that rock was sent flying out into space. About 5 percent of all meteorites that fall to Earth are said to have come from that collision.

Asteroids are fascinating relics of the Solar System, if you've ever wanted to see one now's the time to do it.

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Updates on what's happening at Melbourne Museum, the Immigration Museum, Scienceworks, the Royal Exhibition Building, and beyond.