The night sky: Antarctic crater linked to rise of the dinosaurs

The eastern sky at 8pm tonight.

The eroded remnant of a huge impact crater has been discovered beneath the Antarctic ice sheet in Wilkes Land.

Its estimated age of 250 million years and its 500km diameter make the impact a plausible suspect for the mass extinction that marked the end of the Permian era, when 90 per cent of all species on Earth were wiped out, allowing the dinosaurs to become the dominant land-dwelling animals.

To account for a crater of this size, the object would have had to be about 50km across and would have hit the Earth at a speed of about 30km a second.

Antarctica was once part of the Gondwanaland super-continent; the theory is that the huge hole punched through Earth's crust by this impact triggered the breakup of Gondwanaland into the smaller modern continents around 100 million years ago.

Scientists found the remnant crater by mapping the gravity field using a Nasa satellite.

The idea that impacts by large comets or asteroids cause global mass extinctions is now widely accepted. A buried crater 180km across under the Yucatan Peninsula in Mexico records the impact that probably led to the extinction of the dinosaurs 65 million years ago.

While the cost of drilling through the ice sheet to recover rock samples is prohibitive, rocks from the impact site are carried to the edges of the ice sheet by glaciers and streams. Studying samples collected in this way should enable geophysicists to determine a more precise time for this ancient impact.

Major impacts such as this have been observed. In 1994 astronomers watched as Jupiter's gravity captured a comet, causing it to break apart into multiple fragments. Each fragment ultimately crashed into the planet with devastating force.

The giant planet Jupiter is dominating our evening sky. It is the very bright, pale yellow object seen in the east after dark. It is in Libra and leads Scorpius and Sagittarius across the winter sky as the night progresses.

Jupiter, with its banded cloud layers and family of moons, makes a fine sight in a telescope and now is an ideal time to look.

When seen from a dark place away from the city lights, the star clouds of Sagittarius are among the Southern Hemisphere's gems. While they look like clouds, they are actually the light from tens of billions of faint stars crowding the central bulge of the Milky Way.

Mars and Saturn are close together in Cancer but set early in the evening. Venus is brilliant in the eastern sky before dawn.

* Grant Christie is an astronomy researcher who writes a monthly column for the Herald.