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Sciences

Natural history - from animals to minerals, fossils to sea slugs. MV's scientists use the state's collections in important research.

Dawn reaches Ceres

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by Tanya Hill
Publish date
5 March 2015
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When NASA’s Dawn spacecraft is captured into orbit around the dwarf planet Ceres on Friday, March 6, there will be no fanfare in mission control. In fact, the spacecraft won’t even be in radio contact. There’s no need, because Dawn’s path is set – this is a spacecraft unlike any other.

What makes Dawn unique is its ion propulsion system, which gives the spacecraft incredible manoeuvrability. Instead of using large bursts of thrust to get where it’s going, Dawn takes the slow and steady approach. Its ion engine delivers a tiny but continuous thrust that can last for days or weeks at a time.

Over the last two-and-a-half years, Dawn has been slowly reshaping its trajectory to bring it near Ceres and, most importantly, to match the dwarf planet’s speed – Ceres travels around the sun at nearly 64,000 kilometres per hour.

For other planetary missions, entering orbit is make or break. It’s an intense moment that hopefully ends in jubilant celebration when all goes as planned and the spacecraft momentously falls into orbit. But Dawn’s slow approach means that it is now right on course to guarantee capture by Ceres’ gravity.

Dawn is captured by Ceres' gravity The spacecraft’s approach trajectory with the white circles spaced at intervals of one day. This indicates the spacecraft’s speed – the closer the circles, the more slowly Dawn is moving.
Source: NASA/JPL
 

Come Friday, if the spacecraft’s propulsion were to be switched off it would remain under Ceres’ influence but would travel around the dwarf planet in a highly elliptical orbit. So over the next few weeks, Dawn will use its ion thrusters, together with Ceres’ gravity, to slowly draw it into a circular orbit – the first of four such orbital positions around the dwarf planet.

Not for the first time

Ceres is the second object that Dawn has orbited. Between July 2011 and September 2012, Dawn was in orbit around Vesta, which, like Ceres, resides in the asteroid belt located between Mars and Jupiter.

This marks the first time that one spacecraft has been able to orbit two different planetary objects. And it’s only possible because of Dawn’s ion engine.

A spacecraft powered in the usual way, using chemical propellant, would require ridiculous amounts of fuel to carry out such a mission. And even if it was possible for a spacecraft to carry that much fuel on-board, the cost of the mission would be astronomical.

Dawn's path to Ceres Dawn was launched in September 2007 and has taken the slow and steady approach to visit Vesta and now Ceres.
Source: NASA/JPL
 

At Ceres, Dawn will eventually travel in a polar orbit, travelling above the north and south poles. As it moves from north to south it will travel over the daytime side of the planet, and then during the second half of its orbit it will fly above Ceres' night side.

In its first orbital position, at a height of 13,500km, it will take 15 days for Dawn to complete one orbit. Since the planet takes only nine hours to rotate on its axis, this will allow Dawn to make a good map of the dwarf planet’s surface.

Throughout its 15-month mission, Dawn will vary its orbit three times, each one descending closer to the planet at heights of 4,400 km, 1,470 km and 375 km. To change orbits it will move through a complex series of spiral trajectories.

The descent to its lowest orbit will take two months and, during that time, Dawn will complete 160 revolutions as it constantly reorientates itself to ensure that one of its ion beams is thrusting in the right direction to continue its slow spiral descent.

Dawn's spiral descent Two months of downward spirals are needed to move Dawn into its lowest orbit - from the High Altitude Mapping Orbit (HAMO) to the Low Altitude Mapping Orbit (LAMO).
Source: NASA/JPL
 

Better than Star Wars

Ion propulsion systems, like the one that powers the Dawn spacecraft, have long been considered the next big thing for space exploration. In fact, they seemed so futuristic that they appeared in the Star Wars movies, powering Darth Vader’s TIE fighters or Twin Ion Engine fighters.

Science fiction to science fact The TIE fighters in Star Wars had twin ion engines, but Dawn does one better, with three ion engines.
Source: NASA/JPL
 

Ion engines were first used by NASA on Deep Space 1, which flew past the asteroid 9969 Braille in 1999 and comet Borrelly in 2001.

The Japanese Aerospace Exploration Agency (JAXA) has successfully used ion engines on its Hayabusa asteroid missions, the second of which was launched in December last year.

The Dawn spacecraft is fitted with three ion engines, although only one engine is used at any one time. And true to what we expect from science fiction, the spacecraft does emit a blue-green glow. This is a result of its xenon fuel.

The inner workings of an ion propulsion system. The inner workings of an ion propulsion system.
Source: NASA
 

Positively-charged xenon ions pass through two electrically charged grids. This accelerates the tiny ions and they shoot out of the engine at 144,000 kilometres per hour, providing the thrust to propel the spacecraft in the opposite direction.

Ion engines are around ten times more efficient than chemical rockets because the ions are ejected at roughly ten times the speed that a propellant is expelled by a rocket. The acceleration, however, is much slower.

It would take Dawn around four days to accelerate from 0 to 100 kilometres per hour but the trade off is that in doing so, it would only use 450grams (or just one pound) of fuel.

Why Vesta and Ceres?

Of course, the reason the technology is so marvellous is because it enables such fantastic science – the exploration of the two most massive objects in the asteroid belt, Ceres and Vesta.

The dwarf planet Ceres New images of Ceres, taken February 19 at a distance of 46,000km, show a mysterious double bright spot.
Source: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
 

Don’t let their location fool you – these are not space rocks like typical asteroids. They are big worlds and, like Earth and the other terrestrial planets, Ceres and Vesta have a layered structure.

Vesta has an iron-rich core, a silicate mantle and a crust made of basalt. While Ceres is thought to have a rocky core, an ice mantle and a dusty surface.

The ice mantle is particularly interesting. It’s thought that around 30% of Ceres’ mass may come from water and potentially some fraction of that could be liquid water. Just last year, the Herschel Space Observatory made detections of what appear to be plumes of water vapour escaping from slightly warmer regions on Ceres.

The Dawn mission will continue until June 2016 and the latest images will be regularly posted here, while the Dawn mission blog is a great way to keep up-to-date on everything that happens.

Dawn of the Solar System

The space mission was called Dawn because if we think of Ceres and Vesta as protoplanets, then by better understanding these objects, we will gain insight into the early history of our solar system.

Vesta and Ceres size comparisons Ceres and Vesta more closely reflect half-formed planets than space rocks like asteroids.
Source: NASA
 

The planets of our solar system formed by a method of accretion. Starting out as specks of dust that collided and stuck together, they then grew bigger and formed rocks until eventually they were large enough to draw in enough material to form planets.

Vesta and Ceres seemed to have halted mid-way through this process. This is most likely due to the formation of Jupiter. Its gravity may have prevented objects in the asteroid belt from coming together to finish off the planet building.

As a result, Vesta and Ceres provide a unique opportunity for understanding the early formation of the planets, because they came so close to becoming planets themselves.

The early solar system The early solar system was born out of a dusty disc encircling the sun.
Source: William Hartmann. Courtesy of UCLA
 

The ConversationThis article was originally published on The Conversation. Read the original article.

MV's new digital exhibits

Author
by Nicole K
Publish date
5 March 2015
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On Tuesday 3 March, Museum Victoria joined 25 Australian cultural institutions at Parliament House to launch the Australian component of the Google Cultural Institute.

Google Cultural Institute launch, 3 March 2015, Parliament House, Canberra Google Cultural Institute launch, 3 March 2015, Parliament House, Canberra
Image: Nicole Kearney
Source: Museum Victoria
 

The Google Cultural Institute is an online collection of millions of cultural treasures from over 670 museums, art galleries and archives around the world. Visitors can explore millions of artworks and artefacts in extraordinary detail, create their own galleries and share their favourite works.

Museum Victoria has been involved in the Google Art project since 2011 and was among the first institutions to partner with Google to create what is now the world's largest online museum.

Featured content on the Google Cultural Institute Featured content on the Google Cultural Institute
Source: Google
 

Tuesday's launch welcomed 14 new Australian contributors, including the Australian War Memorial, the National Portrait Gallery and the Australian Centre for the Moving Image. Over 2000 of Australia's finest cultural works are now accessible online.

Among these treasures are 226 highlights from Museum Victoria's collection. These include Aboriginal bark paintings, photographs depicting early Victorian history, and scientific illustrations that trace the development of scientific art.

In order to tell the fascinating stories behind these collection items, we have created three digital exhibitions within the Google Cultural Institute:

The Art of Science: from Rumphius to Gould (1700-1850)

The Art of Science exhibit The Art of Science exhibit
Source: Museum Victoria
 

Scientific Art in Victoria (1850-1900)

Scientific Art in Victoria exhibit Scientific Art in Victoria exhibit
Source: Museum Victoria
 

A.J. Campbell (1880-1930)

A.J. Campbell exhibit A.J. Campbell exhibit
Source: Museum Victoria
 

These exhibits include stunning photographs and illustrations, curator-narrated videos and in-depth information.

Many of these illustrations come from rare books preserved in our library and, in many cases, accompany the first published descriptions of our unique Australian fauna. The books are available online in their entirety in the Biodiversity Heritage Library, a project funded in Australia by the Atlas of Living Australia.

Predator vs predator

Author
by Patrick
Publish date
9 February 2015
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Museum Victoria Bioscans and other biodiversity surveys tend to focus on the bigger and more spectacular Victorian animals, such as Gippsland Water Dragons and Wedge-tailed Eagles, but some of the most interesting stories come from the little creatures. 

Spider wasp nest A partially opened nest of a spider wasp (Fabriogenia sp.). The spider prey in two of the cells have been replaced with wasp pupae.
Image: Patrick Honan
Source: Museum Victoria
 

One such highlight of the recent Gippsland Lakes Bioscan was a mud nest of a spider wasp (Fabriogenia sp.). The nest comprised six cells, each built to house a Mountain Huntsman (Isopeda montana). The cells are made from dried mud, probably mixed with eucalyptus resin to harden them. The female wasp takes about one day to construct each cell, then heads off to find a live huntsman and undertakes a life-or-death battle. Upon seeing an approaching spider wasp, a huntsman’s behaviour—excuse the anthropomorphism—is best described as a ‘mad panic’.

black wasp Adult female spider wasp, Fabriogenia sp.
Image: Patrick Honan
Source: Museum Victoria
 

The wasp is swift and deadly accurate, stinging the huntsman to immobilise it, then removing each of its legs at the first joint. She carries the spider back to her nest, lays an egg on its defenceless body, then seals it in. The egg hatches into a fat wasp grub, feeding on the internal juices of the spider until nothing but a shrivelled husk remains. The grub then forms a pupa and eventually emerges from its cell as an adult wasp, ready to continue the cycle.

Huntsman spider with no legs A dismembered huntsman removed from the mud nest. The pedipalps remain intact and the fangs are in working order.
Image: Patrick Honan
Source: Museum Victoria
 
 
Most members of this wasp family, the Pompilidae, leave the spider intact and paralyse it permanently. In this case, not only does the wasp cut off its prey’s legs, but the venom seems to immobilise the huntsman only temporarily and the spider wakes up after the cell is sealed. 

 

On a personal note, having handled spiders for more than 30 years and never being bitten, one of the spiders latched on to my finger while I was examining the nest. Like most huntsman bites there were no symptoms other than a sharp nip, and given its situation I couldn’t really blame it.

Spider wasp, spider, and spider-wasp mimicking beetle Left: Another member of the Pompilidae, the Zebra Spider Wasp (Turneromyia sp.) battles a huntsman on a gum tree in Royal Park, Melbourne. | Right: Wasp-mimicking Beetle (Trogodendron fasciculatum), also photographed in Royal Park, Melbourne.
Image: Patrick Honan
Source: Patrick Honan
 

And as a side note, spider wasps are ferocious enough to have their own mimics. The Wasp-mimicking Beetle (Trogodendron fasciculatum) looks roughly like a spider wasp, with its black and white body and orange antennae, but its behaviour is almost identical. Moving rapidly over tree trunks with twitching antennae it would, at least, be safe from roaming huntsmans.

The bountiful Mallee

Author
by Patrick
Publish date
17 December 2014
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In Bugs Alive! you can see almost 50 displays of live invertebrates. Most of them from either tropical or arid parts of Australia, illustrating the adaptations needed for living in extreme environments.

Blue butterfly and bee fly resting on grass stems Sleeping beauties, clothed in condensation in the early hours of the morning. | Left: Common Grass Blue (Zizina labradus) Right: A bee fly (Family Bombyliidae)
Image: Patrick Honan
Source: Museum Victoria
 

So each year, when the weather conditions are right, we head out to the Mallee to boost our stocks of insects and spiders. The best time to visit is on a hot, humid night—which happened last week—just before or just after a thunderstorm. Like most desert species, Mallee insects wait months for the rain and then emerge from the spinifex in their thousands.

Two people in arid landscape Chloe Miller and Maik Fiedel searching through typical Mallee habitat.
Image: Patrick Honan
Source: Museum Victoria
 

At night the desert resonates with the songs of katydids, the loudest of which come from Robust Fan-winged Katydids (Psacadonotus robustus). Unfortunately the fat abdomen of this dun-coloured species is often host to the larvae of tachinid flies (family Tachinidae). These parasites feed on the internal organs before emerging from the katydid which dies soon afterwards.

Brown katydid grasshopper A male Robust Fan-winged Katydid (Psacadonotus robustus).
Image: Patrick Honan
Source: Museum Victoria
 

Most katydid species are surprisingly colourful, sporting bright greens, blues and reds.

Three katydid grasshoppers Left: Female Striped Polichne (Polichne argentata); Centre: The undescribed ‘Mystery Hump-backed Katydid’ (Elephantodea species); Right: The unfortunately-named Victorian Sluggish Katydid (Hemisaga lanceolata).
Image: Patrick Honan
Source: Museum Victoria
 

One of our prime targets is Mitchell’s Cockroach (Polyzosteria mitchelli) which we breed at Melbourne Museum off-display, perhaps the most beautiful cockroach in Australia. With its golden markings and eggshell-blue legs, this species is one of more than 500 native cockroaches that are rarely seen by the average Australian but which are extremely important in native ecosystems. They shouldn’t be confused with the five or so introduced cockroach species that infest our houses–native cockroaches are happy in the bush and almost never come inside.

colourful cockroach A female Mitchell’s Cockroach (Polyzosteria mitchelli)
Image: Patrick Honan
Source: Museum Victoria
 

The desert seems to wake up after a rainstorm, with unexpected species such as snails and damselflies making an appearance.

Damselfly and group of snails Left: A female Metallic Ringtail damselfly (Austrolestes cingulatus). Right: Tiny desert snails (Microxeromagma lowei) living under bark.
Image: Patrick Honan
Source: Museum Victoria

Wolf spiders are the dominant ground species, their emerald eyes shining in the torchlight. This male wolf spider (below) was seen halfway down a burrow and was difficult to distract until we discovered the source of his interest—a large female wolf spider at the bottom of the burrow.

Wolf spider and burrow Left: A male wolf spider (LycosaRight: Close-up of the male.
Image: Patrick Honan
Source: Museum Victoria
 

The Little Desert, Big Desert, Sunset Country and Hattah-Kulkyne each have their own distinct habitats and faunas, just a few hours’ drive from Melbourne.

Landscape with blue sky The endless sky and flat horizon of the Mallee region.
Image: Patrick Honan
Source: Museum Victoria
 

Dinorama ready for summer

Author
by Adrienne Leith
Publish date
12 December 2014
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Museum Victoria’s Senior Palaeontologist, Dr Tom Rich, says ‘most people don’t realise that Victoria looked completely different 120 million years ago. If you wanted to you could walk all the way to Antarctica. The vegetation was lush and green. During the winter, it was dark all day. This was the world of the polar dinosaurs that once roamed Victoria.’

It's a world that we're recreating in miniature through our Dinorama – a diorama of the rift valley in southeastern Australia during the Cretaceous period. Our preparators drew from the work of the museum’s palaeontologists and key artists, such as Dr Rich and Peter Trusler, to model the ancient landscape from styrofoam.

Two men in workshop Preparators Kim Haines and Brendon Taylor survey and discuss their progress on the Dinorama.
Image: Adrienne Leith
Source: Museum Victoria
 

Man building a diorama in a workshop Kim Haines sanding the waterways of the diorama.
Image: Adrienne Leith
Source: Museum Victoria

Man painting diorama in workshop Brendon Taylor putting the final touches on the diorama.
Image: Adrienne Leith
Source: Museum Victoria
 

The preps sanded and painted the diorama to create the detailed waterways of the valley. Preparator Brendon Taylor also painted a backboard to show the sky and give the diorama depth.

Apart from adding the last touches of some vegetation, the diorama is now ready for the foyer in anticipation of our summer holiday program. Come to Melbourne Museum in the summer holidays to help populate the Dinorama with miniature animals from the period. 

The Dinorama activity will run daily from 11am to 3pm from 26 December to 27 January.

Links:

MV Blog: Dinosaur diorama

School Holiday activities at Melbourne Museum

Dinosaur diorama

Author
by Adrienne Leith
Publish date
18 November 2014
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Adrienne creates and presents public programs at Melbourne Museum.

Imagine a Victorian Cretaceous rift valley complete with river bed, trees and a suite of prehistoric animals. Now imagine it recreated in miniature in a classic museum diorama: the DINORAMA!

Displayed in front of the Forest Gallery, the Dinorama will be the feature activity of our summer school holidays at Melbourne Museum. We're inviting visitors to make thousands of Cretaceous animals to fill the little landscape with life.

model of dinosaur Serendipaceratops arthurcclarkei was a horned dinosaur, fossils of which were found at Kilcunda. Kim Haines made this tiny version.
Source: Museum Victoria
 

In consultation with our palaeontologists, our preparators made miniatures of three animals—Koolasuchus cleelandi, Serendipaceratops arthurcclarkei and Qantassaurus intrepidus—that lived in Victoria approximately 120 million years ago. From the models, the preparators make moulds…. and from the moulds, summer visitors can create thousands of little beasts from modelling clay.

model of dinosaur Michael Pennell's model of Koolasuchus cleelandi, a three-metre-long predator that lived in and around fast-flowing cold streams. Fossils of Koolasuchus were were found on the coast of Victoria just east of Phillip Island.
Source: Museum Victoria
 

Every couple of days we'll bring out a new colour of clay until we have a Dinorama filled with multi-coloured ancient animals. Our school holiday activities start on 26 December, so keep an eye on the Melbourne Museum foyer after then.

modelling a dinosaur Inverloch was the discovery site of Qantassurus intrepidus, a small herbivorous hypsilophodontid with large eyes for foraging in long polar winters. Brendon Taylor created this model. You can see an animatronic Qantassaurus in the 600 Million Years exhibition.
Source: Museum Victoria
 

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