“Space is big. You just won’t believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it’s long way down the road to the chemist’s, but that’s just peanuts to space.”
So wrote Douglas Adams in A Hitchhiker’s Guide to the Galaxy.
Our ancestors may have had a much better appreciation of just how big the night sky is than we do today because they didn’t have light pollution blocking their view.
But they also didn’t have the telescopes, radio dishes, spectrometers, and satellites extending their view. Nor did they have the understanding of physics, chemistry, and astronomy, which illuminate our knowledge of the cosmos.
Standing in an Agora in Athens, 2500 years ago, would an ancient Greek imagined one day we would send probes to meet with asteroids? Or that the probes would be able to pick up material from these asteroids and return it to Earth?
Two weekends ago, Japan’s space agency retrieved a capsule released from the space probe Hayabusa2 containing uncontaminated samples from the asteroid Ryugu. This concluded a six-year mission, which saw the probe travel 5.25 billion kilometres to the asteroid and back (the equivalent of 131,250 trips around Earth.)
Ryugu is a dark, carbon-rich rock a little more than half a mile wide. Yet the sample from its surface should help to shed light on the earliest eons of our solar system. It might even provide some clues as to the chemical composition of the early Earth and tell us about the origins of life.
And which astronomer standing on an Aztec pyramid 1,500 years ago would have thought a giant space telescope would one day occupy nearby islands and reveal the depths of the universe?
The Arecibo radio telescope in Puerto Rico was the second largest radio telescope in the world. I say ‘was’ because it had been falling apart over the past several months, a victim of benign neglect and an unwillingness to keep the facility looking at the universe. Two of the cables connected to the support towers gave way a few months ago and the whole facility began to unravel. Finally, the instrument platform gave way, plummeting 137 metres into the reflector dish below. After 67 years of service, it had met its demise but during its life it had given us so much.
In 1970, Arecibo took the first pictures of the surface of Venus. Using radar to penetrate the hellish atmosphere filled with carbon dioxide and opaque to optical telescopes, it was able to map the highly reflective Alpha and Beta regions, along with the huge Maxwell Montes mountain chain. In 1988, using electromagnetic waves across several polarizations, Arecibo showed us just how different and complex Venus’ surface really is. It allowed us to go to a place where we had never gone before.
But Arecibo was also the telescope that discovered the pulsar at the heart of the Crab Nebula in 1968 and a binary pulsar in 1974, explaining the fate of stars. It measured the 21-cm line for hydrogen, which allowed astronomers to calculate how fast galaxies rotate and how far away they are. Arecibo’s observation of galaxies in the Pisces-Perseus supercluster generated the first three dimensional map of the massive string-like structure of galaxies. And its observations confirmed the loss of energy by gravitational radiation as predicted by Einstein’s General Theory of Relativity.
And what child looking up at the night sky in 1969 would have imagined we would now be able to construct a map of the Milky Way showing us where thousands of stars have been and perhaps more importantly, where they are going?
In 2013, the European Space Agency launched the Gaia space observatory. Its mission was to travel to a point 1.5 million miles from Earth, called a ‘Lagrange point’, and perch there for a decade generating the best atlas of the stars possible.
Tracking over 1 billion stars in our galaxy, the observatory slowly spins, allowing it to measure the same stars many times and over long periods. Further, because it is tied to the Earth and the Earth orbits the sun, it is able to obtain pictures of the stars across a base-line which is 300 million kilometres wide. This results in parallax – tiny shifts in the position of stars against a static backdrop – which provides for precise measurements of distance.
By utilizing the deep field images of distant galaxies as a constant reference, Gaia has obtained precise measurements of both the distance to 400,000 stars and their apparent motion. For stars within 5,000 parsecs or 16,000 light years of Earth, it can measure distance with an accuracy within 10 per cent. And for the 300,000 objects within 300 light years, the data is even better.
Space is big. But we have learned so much over time and we will keep on exploring.
