New Technique to Accurately Measure Asteroids

Article written: 4 Feb , 2009
Updated: 24 Dec , 2015

It’s one thing to know the position of an asteroid out in space. It’s quite another to know the size and shape of a particular asteroid that might be heading our way. A team of French and Italian astronomers have devised a new method for measuring the size and shape of asteroids that are too small or too far away for traditional techniques by using ESO’s Very Large Telescope Interferometer (VLTI). This will increase the number of asteroids that can be measured by a factor of several hundred, and provide the ability to resolve asteroids as small as about 15 km in diameter located in the main asteroid belt, 200 million kilometers away. This is equivalent to being able to measure the size of a tennis ball a distance of a thousand kilometers.

“Knowledge of the sizes and shapes of asteroids is crucial to understanding how, in the early days of our Solar System, dust and pebbles collected together to form larger bodies and how collisions and re-accumulation have since modified them,” says Marco Delbo from the Observatoire de la Côte d’Azur, France, who led the study.

Direct imaging with adaptive optics on the largest ground-based telescopes such as the Very Large Telescope (VLT) in Chile and space telescopes, or radar measurements are currently the best methods of asteroid measurement. However, direct imaging, even with adaptive optics, is generally limited to the one hundred largest asteroids of the main belt, while radar measurements are mostly constrained to observations of near-Earth asteroids that experience close encounters with our planet.

Another double asteroid. Credit: ESO

Another double asteroid. Credit: ESO

Delbo and his colleagues have devised a new method using interferometry that will not only increase the number of objects that can be measured, but, more importantly, bring small asteroids that are physically very different from the well studied larger ones into reach.

The interferometric technique combines the light from two or more telescopes. Astronomers proved their method using ESO’s VLTI, combining the light of two of the VLT’s 8.2-metre Unit Telescopes.

“This is equivalent to having vision as sharp as that of a telescope with a diameter equal to the separation between the two VLT Unit Telescopes used, in this case, 47 meters,” says co-author Sebastiano Ligori, from INAF-Torino, Italy.

The researchers applied their technique to the main belt asteroid (234) Barbara, which was earlier found, by co-author Alberto Cellino, to have rather unusual properties. Although it is so far away, the VLTI observations also revealed that this object has a peculiar shape. The best fit model is composed of two bodies each the size of a major city – with diameters of 37 and 21 km – separated by at least 24 km. “The two parts appear to overlap,” says Delbo, “so the object could be shaped like a gigantic peanut or, it could be two separate bodies orbiting each other.”

If Barbara proves to be a double asteroid, this is even more significant: by combining the diameter measurements with the parameters of the orbits, astronomers can then compute the density of these objects. “Barbara is clearly a high priority target for further observations,” concludes Ligori.

The team will now begin a large observing campaign to study small asteroids.

Source: ESO

14 Responses

  1. Theta says

    “This is equivalent to having vision as sharp as that of a telescope with a diameter equal to the separation between the two VLT Unit Telescopes used, in this case, 47 meters,”

    Wait… woah. Woulden’t that have applications way beyond just asteroids?

  2. Theta says

    Cool indeed!

  3. Ron says

    Yes! Interferometry is the future of astronomy. It’s not really a new technique, just in its application to imaging asteroids. Interferometry can also be used to detect gravity waves created by cataclysmic events such as supernovae, neutron stars colliding, etc. as predicted by relativity. Pretty cool stuff!

  4. Member
    Jon says

    Do gravity waves dissipate?

  5. Jorge says

    And now just imagine what we’d be able to see with two space telescopes, placed in Earth’s L4 and L5 Lagrange points. They wouldn’t even have to be large. Imagine what could be resolved by a telescope with a diameter of 1AU.


  6. Rob says

    Lagrange points.. 1 AU telescope.

    Well, the problem is that the two (or more) telescopes has to be connected through one or more optical waveguides to provide for interferometric measurements. An 1 AU long fiberoptic cable would be easier to produce than a 1 AU wide telescope, but anyway..

    I guess the technique is new for Asteroids as these are very faint objects and therefore require very large optical mirrors (i.e. VLT).

  7. robby says

    Jorge=Lets just hope they can get a replacement for the 2.4m HST before it becomes too expensive to easily repare due to the harse environment it’s in besides the dangers of space junk. A 10meter would be
    a great replacement. The Earth-Moon L5 area, I think would be very suitable to place a series of tracking satillites for near zero albedo comets-asteroids ‘coming from the direction of the sun’ as things now stands by being ‘blind sided’ by a comet/asteroid.
    To have 2 scopes 1AU apart-Rob is correct on that

  8. Jorge says


    Who said the telescopes have to be linked by fiberoptic? ESA’s Darwin project plans on sending up 4-5 independent satellites who would fly in formation in the area of the L2 point, separated by several hundreds of meters. They seem to be confident in acheiving the level of precision needed to combine light out there without any physical connection between the telescopes. Granted, the same thing in L4 and L5 is in a whole different scale, but, if Darwin is feasible, I can’t see why it can’t be acheived further on.

  9. robby says

    Jorge, I also read reports of the Darwin project and is very possible.The problem is the distances of 1 AU you already stated. IAU is about 250million times further than 500meter U know as distance to star doubles, its 4X dimmer, 10x=100x dimmer and so on. The requirements for something 250M times further is beyond my knowledge or career as I retired 2 years ago as a Network Administrator, but I’m certain this 1 AU separation is many centuries or not ever feasible..However, I do believe the ESA darwin project will work-it will be very tempermental and with teething problems for a while but it will eventually work as planned

  10. Luke Garratt says

    Firstly, wouldn’t it be more than 1AU, as the distance is between the LaGrange points is greater than distance from Earth to the sun? About 1.73?

    Also, I don’t think the problem of distance is an issue. If the two telescopes faced away from the sun in the general direction of earth and focused on objects in that direction, wouldn’t the distance to the object be relatively the same for both the telescopes? Particularly the farther you looked?

    As the telescopes orbit the sun you would sweep the sky

  11. robby says

    Luke , you are on to sometihing , I thought perhaps the Earth-Moon L5 point is 60 degrees fore-aft of the Earths-Moon orbit.
    To have 2 telescopes at the maximum points for the Earth -Moon L5 points would be quite a feat to synchronize them , still, I can’t find any thing much to gain to have 2 scope spread so far apart except to instantly see the parallax of the nearest stars, however, I am now going into something I’m not knowledgeable about ,the technology of
    optical waveguides to provide for interferometric measurements-this is beyond my education or career. Still , thank you much for your reply, There is much I ‘m learning about on this sites feeds,forums, it can be much more technical than the Yahoo StarryNite forum I’m in. lol.

  12. Marco says

    Here is a question about interferomtry and it comes from my profund ignorance on the nuts and bolts of actually doing interferomtry. In order to achieve the effect, do the devices need to be linked in realtime? A large separation, such as 1 AU, makes that difficult. If the individual collections can be recombined at a later time using precise time hacks in the data, then the precision of the connection between the collectors is not that important. That means that one could park collectors any distance apart. Why stop at one AU?

  13. Spoodle58 says

    Great question Marco, hope someone has an answer, I wouldn’t mind knowing myself. 🙂

  14. Marco says

    Spoodle58 – Thank you. It seems we are to remain without an answer.

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