Double Asteroid Redirection Test

Two seconds before impact

Double Asteroid Redirection Test, or DART for short, is an attempt by NASA to redirect the orbit of asteroid Dimorphos via direct impact with a man made spacecraft.

The first image shows the final moment captured by the spacecraft’s camera just 2 seconds before impact with the asteroid’s rocky surface on 27th September. The second image shows a series of recently released James Webb stills of the asteroid at various times after impact.

James Webb images of Dimorphos post impact

The 525 foot wide asteroid is actually a small orbiting chunk of a larger ‘system’ of asteroids some 7 million miles from Earth.

This particular space rock poses no risk to Earth but provides a perfect test of our ability to potentially change the orbit of larger near Earth asteroids that could pose an impact risk in the future.

We won’t know how successful DART has been until November, when all data has been gathered and a new orbit for Dimorphos calculated. DART team members hope to change the orbital period by at least 73 seconds for the mission to be deemed a success.

Constructive destruction.

The Statistics of Large Space Rocks

Jupiter was recently hit by a giant space rock and astronomer @jose.luis_pereira (Instagram) was lucky enough to capture the impact in this incredible footage.

Encounters like this always remind me of our relative fragility on planet Earth. Although Jupiter’s gravity protects us from more frequent large impacts, there’s an inevitability when it comes to future encounters with big space rocks. You need only glance up at the Moon for clear evidence of this destructive heritage.

The statistics of space rock encounters are both reassuring (in terms of long timescales) but also gravely concerning (in terms of raw destructive power).

On average, every few hundred years, the Earth is hit by an object some 30-60 meters in diameter. Such an impact generates enough energy to devastate an entire city if the final shockwave is concentrated in the right position and direction. The 2013 Chelyabinsk and 1908 Tunguska events are recent example of such encounters.

Then every 10,000 years we’re hit by a 200-500 meter wide object, large enough to trigger short term but significant climate changes, potentially lowering global temperatures and disrupting crop growth and finely balanced ecological systems.

Then every million years a 2-4 kilometer wide impact can occur, releasing energy equivalent to the explosive output of every nuclear weapon on the planet!

Finally on a hundred million year timescale Earth can be visited by something like the Chicxulub event that wiped out the dinosaurs, an object some 10-20 kilometres across. That’s enough destructive power to wipe out vast swathes of life across the entire planet.

As a species we’re only a few million years old and our recorded history takes us back a paltry 10,000 years. It makes you wonder therefore, what unrecorded and long forgotten destructive encounters our distant ancestors experienced and survived? Or is our species yet to be challenged by any of the bigger impacts mentioned above?

Changing Sunset Position

 

sunset

Changing position of Sunrise from a fixed location over a year

The changing position of Sunrise throughout a year from a fixed location. The further north or south of the equator we live the more extreme our seasonal changes and the bigger shifts we perceive in the sunrise or sunset position during the year.  In such harsh and changing seasons it would also have been the more important for ancient cultures to mark the seasons.

Using the landscape to mark the seasons like this is called a horizon calendar. But what if your horizons are flat and featureless, or you require more accuracy, or you’re a powerful priest and wish to theatricise important changes in time?

Then ‘perhaps’ you construct an artificial horizon by placing large stones to mark the progress of the Sun – a henge.

Photo Credit: Zaid Alabbdi