While pondering on the NASA mission’s cost some people began wondering why sending New Horizons to Pluto when we have Hubble. Intriguingly, the 25-year-old space telescope can take brilliantly sharp images of remote stars and galaxies, but when it comes to Pluto it can only render a fuzzy space ball.
Researchers explained that the dwarf planet is amazingly closer than those galaxies and supernovas, but it is also incredibly smaller. This may explain why the U.S. government decided to invest into a single robotic spacecraft $700 million a decade ago.
Hubble can get accurate images of space objects located millions of light years away because those objects are considerably larger than Pluto and look brighter on our night sky.
So far, all Hubble’s shots of Pluto, which is just a few light hours away, were blurred and just a few pixels across. Chris Lidman a researcher at the Australian Astronomical Observatory explained that that isn’t the case with remote galaxies since there is a ‘good reason’ for it.
The good reason is called ‘the angular size,’ which is the size of the portion of the night sky a space object covers (as seen from Earth). The angular size is influenced by the space body’s real size and its location.
Lidman also said that those bright galaxies we marvel at when looking at Hubble photos might be millions of light years farther than Pluto, but they are also trillions of times bigger. As a result they have a greater angular size than the dwarf planet.
Yet, two very distant objects can have the same angular size and cover the exact amount of space on the sky. This is the case of the sun and the moon, despite the sun being 400 times farther away than our natural satellite.
Scientists explained that because the two share the exact angular size, total solar eclipses can be possible. Pluto, on the other hand, because it is located so far away has a very small angle. By comparison, a large galaxy that Hubble may focus on, may cover a portion of the sky that is 20 times larger.
This is why NASA had to send a spacecraft all the way to Pluto to get those stunning images of its surface and moons. The photos also helped scientists better understand the nature of the dwarf planet, and adjust their older models to new realities.
“Before New Horizons, Pluto was just a pin prick against a starry backdrop,”
Image Source: Wikipedia