Mission to save the planet
IF you are a driver, you have probably, on many occasions, found yourself driving in the direction of the sun not long before sunset or just after sunrise.
Like me, you will have experienced the difficulty seeing the road and the oncoming traffic — especially, for example, on the Bass Highway, where many sections are oriented east-west.
Extra care is needed to steer your vehicle accurately, and slowing down at those times is very important.
The opposite situation is when you are driving away from the sun’s direction, and the road and oncoming traffic are clearly illuminated. At those times, it’s a good idea to make sure your headlights are on so that the drivers dazzled by the sun can see your location clearly.
You may wonder what connection this has with astronomy. Well, quite apart from the direction of the sun being a very astronomical topic, the equivalent of that driving difficulty happens when trying to observe objects in space.
When astronomers are searching for asteroids that could pose a threat to Earth, those that are in the direction of the sun are harder to spot.
To solve that problem, NASA is planning a new space mission, called NEO Surveyor, with NEO standing for Near Earth Object.
NEO Surveyor will be sent to a stable point known as L1,
about 1.5 million kilometres on the sunward side of Earth. This is in contrast to the L2 location of the James Webb Space Telescope, which is 1.5 million kilometres on the other side, facing away from the sun, to get the best infrared view of the universe.
A NEO is an asteroid or a comet whose path around the sun along its orbit brings it close to Earth. Specifically, its orbital path includes the range of distances from the sun between 98.3 per cent of Earth’s distance and a distance 30 per cent farther out than Earth.
If its orbit is such that it can
currently pass within 7.5 million kilometres of Earth and it is at least 140m across, it is also called a PHO (a Potentially Hazardous Object).
To set your minds at ease, we don’t know of any PHOs that are on a collision course with us over the next 100 years — and the few that will come extremely close to us have very low collision probabilities assigned to them.
Some are smaller than the object about 17m across that exploded over Chelyabinsk in Russia in 2013, though the energy of even that relatively minor impact caused injuries to more than 1000 people because of flying glass from smashed windows.
The problem is that it is estimated that only about 40 per cent of PHOs have so far been found. The most dangerous objects are those at least 1km across, but it is estimated that 10 per cent of these are still to be found, too.
NEO Surveyor is designed to enlarge our knowledge of the existence, size and orbital paths of as many such objects as possible.
Objects that are relatively close to us, and positioned closer to the sun than we are, are viewed mainly from their “night’’ side, because the sun
is mainly illuminating the side of the object that is facing away from us. That makes them harder to spot, because they do not reflect as much light in our direction.
NEO Surveyor will solve this problem by observing in infrared light, to detect the emission of heat from the objects. This is more likely to reveal their presence than simply by observing in normal “white’’ light.
NEO Surveyor will be part of NASA’s planetary defence program, and will cost between about $US500m and $US600m. That may sound like a lot of money, but it is important
to put that into perspective. It represents about 10c Australian for everyone on Earth. Of course, if it came to a worldwide “whip-around’’, not everyone would be able to spare even that amount, but I’d gladly put a dollar or more into the hat if necessary.
A sobering thought is that the cost of NEO Surveyor is far, far less than the resources that humans put into defending themselves against each other.