A dedicated space-based telescope is needed to achieve a congressionally mandated goal of discovering 90% of all near-Earth asteroids down to a size of 140 metres by the year 2020, says a report NASA sent to the US Congress on Thursday. Asteroids of that size are large enough to destroy a major city or region if they strike the planet – but NASA says it does not have the money to pay for the project.
The study says Venus is the best place for the telescope. That is because space rocks within Earth’s orbit – where Venus lies – are most likely to be lost in the Sun’s glare, potentially catching astronomers off guard. The telescope could be placed either behind or ahead of Venus in its orbit by about 60° – the stable Lagrange points, known as L4 or L5, where the gravity of the Sun and Venus are in balance.
“There are quite a few [objects] that are interior to Earth’s orbit,” NASA’s Lindley Johnson told New Scientist. “Those are really hard to detect [from Earth]; the opportunities to see them are very limited.”
From the orbit of Venus, however, “you’re always looking away from the Sun, always looking out”, he says. “And, of course, you can observe 24 hours a day – you don’t have to worry about night and day.” Even from Earth orbit, a telescope’s view of any given part of the sky is blocked about half the time by the Earth itself.
In addition, because Venus orbits the Sun in about two-thirds the time the Earth does, a telescope in that orbit would catch up with any near-Earth asteroids in their orbits more frequently than Earth does, offering more opportunities for discovery. “You’re able to sample that population more rapidly in the same amount of time,” Johnson says.
An infrared telescope would be more effective than one that studies visible light, because asteroids reflect sunlight more strongly at infrared wavelengths. The background sky is also much less bright in the infrared, providing better contrast for discovering even small, faint asteroids.
With the Venus-orbit IR telescope, NASA could exceed its goal by three years, finding 90% of the most dangerous space rocks by 2017. But the space telescope is estimated to cost $1.1 billion for 15 years of operation, and NASA says there is currently no money in its budget to pursue any of the search proposals it studied.
That means it would take until at least 2026 to achieve its goal – and that is assuming a large telescope in Chile called the LSST (Large Synoptic Survey Telescope) is completed. But the LSST, which would be funded through the National Science Foundation, itself has not had final approval (see Unique wide-field telescope will make ‘sky movies’). Without the LSST, the goal would slip beyond 2030.
Former Apollo astronaut Rusty Schweickart says NASA’s analysis was a good examination of the options, and showed that “the space option … is most effective” in dealing with the danger of an unexpected impact.
But Schweickart says NASA failed to deliver on an additional analysis that Congress had asked for, which included an examination of the relative merits of different proposals for deflecting an asteroid found to be on a collision course with Earth. “[NASA] did nothing, they declined to respond. That’s pretty disappointing,” Schweickart told New Scientist.