Two New Asteroids to Pass Earth This Week


Two newly discovered asteroids will pass the Earth this week. The asteroids were discovered on September 5th of this year by Andrea Boattini using the 1.5 metre reflector at Mount Lemmon in Arizona as part of the Mount Lemmon Survey.

These two new asteroids have been given the designations of 2010 RF12 and 2010 RX30. Both are small bodies, which is why they were not discovered until mere days before they would pass the Earth. Estimates put the size of RF12 at 5 – 15 meters with a best estimate being around 8 meters (26 ft). The larger, RX30 is estimated to be 12 meters (39 ft), but the range of estimates go from 7 – 25.

Due to the large range of estimates on sizes, as well as poorly constrained relative velocities and an unknown composition, it would be difficult to predict the damage an impact from these bodies could cause. The majority of the mass for such small objects would burn up in the atmosphere with only small fragments surviving to the ground. For comparison, the estimated size of the object that caused the Tunguska event was estimated to be at least a few tens of meters in diameter at the point it exploded in the atmosphere some few miles up. Since the diameter helps to determine the volume, and thus the mass and kinetic energy, this factor increases the potential damage rapidly. However, although the bodies were just discovered this week, their orbits have already been well established for the near future and neither will collide with Earth. Both are rated at a 0 on the Torino scale (data from NASA’s NEO Program for RF12 and RX30 can be seen here and here respectively).

Although both objects will pass closer to the Earth than the moon, due to their small size, neither will be visible to the naked eye. 2010 RF12 is expected to pass the Earth at 21% of the Earth-moon distance and at maximum brightness, reach only 14th magnitude, which is just over 600 times too faint to see with the unaided eye. RX30 will approach at 66% of the Earth-moon distance and is expected to reach a similar peak magnitude. For those interested in tracking or photographing these objects, the Fawkes Telescope Project has created a page dedicated to these two objects, including best exposure times and filters for cameras that can be found here. Ephemeris for RF12 and RX30 can be found here and here respectively.

Although both of these asteroids were discovered on the same day and will be approaching near the same time, their orbits do not appear to be related. RF12’s orbit extends from 0.82 to 1.17 AU and it orbits the Sun once every year. Predictions have shown it only passes near the Earth once every one hundred years. Initially, RX30 was thought to be rotate extremely fast, but revised observations have shown that it takes at least 6 hours to rotate about its axis.

7 Replies to “Two New Asteroids to Pass Earth This Week”

  1. “it orbits the Sun once every year”. Um, if “year” means “local year”, that’s a tautology …

    Seriously: isn’t the orbital period a function of the semi-major axis, 1.17 AU? So shouldn’t it take substantially longer than an (Earth) year to orbit the Sun?

  2. I was going with year being defined as an Earth-year. You’re right about the period. I hadn’t looked to see what the semi-major axis was and just took the press-release’s word for it. I’ll have to look at it a bit more.

  3. @ JON VOISEY,

    Correct me if I’ve missed something, as this is just a back-of-the-envelope calculation, but going by the figures you stated above for RF12’s orbit — 0.82 AU at perihelion; 1.17 AU at aphelion — then its semi-major axis is approximately:

    (0.82 + 1.17) / 2 = 0.995 AU.

    So, according to Kepler’s third law of planetary motion, symbolically:

    T^2 ∝ a^3

    where T is the orbital period (Earth-years) of the object and a is the semi-major axis (AU) of the orbit.
    So, the orbital period of RF12 should be approximately:

    √0.995^3 = 0.99251 yrs. (362.5 days).

  4. These Aten objects have surprisingly large deltas in orbital velocity based on planetary and solar encounter perturbations. They come by earth at anywhere from 8 km/sec to 25 km/sec … current encounters will be near the top of that range. If they are stony asteroids this means to me that an impact encounter with them would be pretty “hot” and result in an airburst disintegration … possibly not unlike Tunguska. I doubt if azimuth angle would change much except the altitude at which the airburst occurs. Just thinking out loud …

  5. “0.82 AU at perihelion; 1.17 AU at aphelion — then its semi-major axis is approximately: (0.82 + 1.17) / 2 = 0.995 AU.”

    To unpack that for any other novice who was as confused as I was: the major axis is the axis that pases the long way through the ellipse (through both foci), and the semi-major axis is half that. For one body (this asteroid) orbiting a much more massive body (the Sun), the massive body is at one focus of the ellipse. So, as shown with the diagram at wikipedia’s article “Apsis”, periapsis is the closest approach to the big body, and apoapsis is the farthest distance, and those two points are the end points of the major axis. So “The arithmetic mean of the two limiting distances is the length of the semi-major axis”. Hence (0.82 + 1.17) / 2 = 0.995 AU, very nearly a year.

    My apologies. I had somehow gotten the impression that the apoapsis distance alone was the semi-major axis. I blush.

  6. Diameter determines volume and mass? What about density? My understanding was that the density of the Tunguska impactor was low.

  7. p = m/v. The three are related. Pick two and you find the 3rd. I just went with the ones that are functions of diameter (although it’s arguable that it’s not really since asteroids don’t have to be very round, but to a loose estimate, I went with it).

    And yes the Tunguska meteor was low density. Had it been higher, it would likely not have exploded in the atmosphere.

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