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Chinese Mission to an Earth Co-Orbital

This morning’s entry resonates with Jim Benford’s recent work on objects that are co-orbital with Earth (see A SETI Search of Earth’s Co-Orbitals). You’ll recall that Benford argues for close study of co-orbitals like Cruithne (3753), a 5-kilometer object with closest approach to Earth of 0.080 AU, and 2010 TK7, which oscillates around the Sun-Earth Lagrangian point L4. A number of other such objects are known in a 1:1 orbital resonance with Earth, but they are seldom studied or even mentioned in the literature.

Calling for SETI observations at radio and optical wavelengths, as well as lighting up the objects with planetary radar, Benford gives a nod to Ronald Bracewell, who speculated that one way for an extraterrestrial intelligence to study a stellar system would be to plant a probe within it that could inform the home civilization about events there. The Earth co-orbitals are made to order for such observation, so why not give them a look with all the tools in our SETI arsenal?

Now we learn that China plans to explore the near-Earth asteroid 2016 HO3, along with a main-belt comet designated 133P. An interesting move — 2016 HO3 is the closest, most stable quasi-satellite of Earth, with a minimum distance of 0.0348 AU. Also known as Kamoʻoalewa — a Hawaiian word for an oscillating object in the sky — 2016 HO3 has a minimum orbital intersection distance of 0.0348 AU (5,210,000) km, which is 13.6 times as far away as the Moon, although it seldom comes closer than about 38 lunar distances from us. The Center for Near Earth Object Studies (CNEOS) calculates this one has been in a stable orbit of our planet for about a century and will remain in its orbital pattern for centuries.

Image: Orbit of 2016 HO3. Credit: James Benford.

According to Liu Jizhong, director of the Lunar Exploration and Space Program Center of the China National Space Administration (CNSA), the current plan is to study 2016 HO3 from space before landing on it to collect samples for return to Earth. Following delivery of the sample return capsule, the probe is to proceed to comet 133P by means of gravity assists at Earth and Mars, in a mission lasting on the order of 10 years.

China is now soliciting proposals for eight types of scientific instruments for the mission among universities, research organizations and private companies both in China and abroad, according to a CNSA news release. Among the instruments needed, Liu says, are a color camera with an intermediate field of view, thermal emission spectrometer, visible and infrared imaging spectrometer, multispectral camera, detection radar, magnetometer, charged and neutral particle analyzer and dust analyzer. Quoting from the news release:

[Liu] said there might be two forms of onboard schemes. One possible scheme is to carry an independent detector on the rocket. After China’s main probe enters the orbit, the onboard detector will separate from the rocket and then perform independent tasks. Its mass should not exceed 200 kg. The other possible option is to let China’s main probe carry the onboard detector to the near-Earth asteroid or the main-belt comet and then release it. The detector could either perform independent scientific exploration or coordinate with the main probe.

If the onboard detector does not separate with the main probe, its mass should not exceed 20 kg. If the detector separates from the main probe near the asteroid, its mass should be no more than 80 kg. If it separates from the main probe near the comet, its mass should not exceed 20 kg.

The deadline for proposals is August 31, 2019, with those interested asked to contact CNSA.

Image: An animation of 2016 HO3’s orbit around Earth 2000-2300. Credit: Phoenix7777 – Own work. Data source: HORIZONS System, JPL, NASA. CC BY-SA 4.0.

This will not be China’s first experience with an asteroid mission. In December of 2012, its second lunar probe, Chang’e-2, made a close approach and flyby of asteroid 4179 Toutatis after completing its primary mission, approaching to within 3.2 kilometers and returning images. Now we have an ambitious mission to give us a close-up look at an Earth co-orbital, with comet operations to follow. We should learn a lot, for right now even the size of 2016 HO3 is not firmly established, though it is believed to be between 40 and 100 meters, depending on assumptions about its albedo, and we do know that it is a fast rotator.


Comments on this entry are closed.

  • Bruce D. Mayfield April 22, 2019, 11:36

    It’s great to see that this object will be getting some close attention. And WHAT an interesting orbit! The timing of this object’s peculiar orbit is interesting too, bracketing the dawn of our space age. But surely that’s merely coincidence … ?

  • John walker April 22, 2019, 15:59

    Not wishing to second guess an unknowable alien intelligence, I do however, doubt the practicality of NEOs or “co-orbitals” as priority targets for eti Earth observatories.

    The most practical location for such an outpost is on the object of interest itself not millions of kilometers distant. I am curious to hear speculation as to why this would not be considered best. To avoid long term instrument degradation in a corrosive climate or perhaps inadvertant and unwanted “discovery” by a native inferior intelligence. Even with our technology we are nearing the capability to prevent both these hazards. Nevertheless, if for whatever reason a base on the native world is regarded as inappropriate, then a nearby space based platform would be the next best though magnitudes worse position. And if not space based then lunar. Resources for basic needs such as power and self repair are available everywhere. A co-orbital low g rock offers only a modicum of extra anonymity compared to these other options. Is there another important benefit to these more distant objects that would render them superior?

    • Bruce D. Mayfield April 22, 2019, 18:14

      Those are very valid points John. Another factor against using 2016 HO3 as platform for Earth surveillance is its rapid rotation:
      “Photometric observations in April 2017 revealed that Kamo‘oalewa is a fast rotator. Lightcurve analysis gave a rotation period of 0.467 ± 0.008 hours (28.02 ± 0.48 minutes) and a brightness variation of 0.80±0.05 magnitude (U=2).[5][b]”
      Imagine the difficulty of spying on any given location on Earth from such a moving platform. The near side of our Moon would be enormously better for Earth recon.

      • Michael C. Fidler April 22, 2019, 22:09

        What would the G force be on the inside of a hollow sphere 130 to 330 feet in diameter rotating in 28 minutes?

        • Ron S. April 23, 2019, 9:14

          You want the standard formula for a centrifuge. Unless I made an error, for a 50 meter radius and 28 min rotation the acceleration is approximately 0.378 g.

          • Ron S. April 23, 2019, 9:19

            Oops. Got my units wrong. I thought my number looked awfully large. Revision is 0.000067 g. But maybe I made another mistake.

        • Alex Tolley April 23, 2019, 11:02

          Between 0.00003 to 0.00007 g

          accn = v^2/r
          r = 65ft ~= 20m
          28 mins = 1680s

          v = 2(pi)r/t
          accn = 4(pi^2)r/t^2
          g = 4(pi^2)r/(9.81 (t^2)))

          Despite the nomenclature, 28 minutes is very slow for creating artificial g in a rotating body. If you recall from the movie, 2001: A Space Odyssey, space station V was rotating every few seconds with a much larger radius to generate the g experienced. You can see this when Floyd is making a call to his daughter.

          Centripetal Force

    • Michael C. Fidler April 22, 2019, 20:19

      Well it could be an intergalactic cruise ship and they just send the tourist down in smaller craft!

    • Curious April 22, 2019, 21:35

      I agree, why wouldnt it be on the target planet itself. Some ideas to consider:

      Pros for putting probe on the target planet:
      1) A hospitable planet would presumably have more moderate temperature/pressure/chemical/radiation environment, so if life can exist there the probe certainly should.
      2) I think it is reasonable to consider that such an ET probe could be exceedingly small. Imagine how easy it would be to hide say a baseball sized probe somewhere on earth.
      3) Can directly sense planets conditions with the simplest sensors, perhaps even the civilization’s sniff RF signals and communications to study them and their intents
      4) You can employ aerobraking on a planet with atmosphere. An ET probe could realistically be assumed to be capable of performing its own entry/descent/landing by real-time sensing of atmosphere, without the foreknowledge/entry modelling like we do today. Imagine the computing/AI horsepower we will be capable of in say another 50 years of technological advances
      5) Power – a habitable planet would presumably have some sources usable for power that the probe can harness, solar, chemical, thermal, maybe even directly tapping electrical power grids, or high frequency signals. Again imagine what 100 years of technical development might allow us. “Machines” at the nano level perhaps emulating biological processes for energy conversion. Look what a simple beetle can do with crude resources.

      Pros for putting off the target planet:
      1) A known environment for the probe – design it for space vacuum and radiation and some solar power
      2) Anonymity – physically and for ET communications to its homeworld. At least until the target planets civilization advances sufficiently to look for you like we are now. Especially if the probe is large, or the transmitter to the ET homeworld is. Could we have detected regularly occurring light or xray transmissions off these coellipticals say 50 years ago?
      3) On a smaller body the gravity well is easier to depart from if you intend that at some point.

      • Paul451 April 23, 2019, 9:08

        The original idea for a Bracewell Probe is as a relay between sentient races. It’s not meant to be active until a local intelligent race reaches radio-civilisation level.

        The concept attempts to assume the fewest technological advances needed to achieve the goal. Hence little or no AI. No assumption of miniaturisation. No ability to survive on Earth for millions of years. And a deliberate avoidance of any sentient species while they are developing.

        As for residing on the moon, it’s senders wouldn’t know about the moon before sending it. As for “energy”, it is sited for continuous solar power, obviously.

  • Michael C. Fidler April 22, 2019, 22:04

    1. Do they have any planned launch date?

    2. Is this easier to reach then the moon?

    3. Could it be worth mining and how hard to bring it into lunar orbit?

    • Alex Tolley April 22, 2019, 23:16

      If the 100 m diameter is used, it would be about 1 million tonnes. That would be far too hard to move to another orbit. Recall that the now abandoned NASA ARM mission was for an asteroid of perhaps 10 m or less in diameter (1000 tonnes max).

      Whether it is worth mining might be answered when the sample return is done. Then the possible resource and costs would be better understood. I think there are better NEO targets for possible mining.

      What I find more intriguing is the same argument for locating a Bracewell probe in these orbits may be the same for terrestrial nations. Good platforms to make covert observations with advanced technology, perhaps in concert with small satellites in orbit, yet distant and protected enough to avoid being targeted by ground or space-based weapons. While I don’t think they would be useful as “high ground” missile platforms, they just might be useful for high powered lasers.

  • Gary Wilson April 23, 2019, 12:41

    What about the possibility that we’ve been visited and rejected as an interesting Bracewell probe destination? Aliens discussing us based on their most recent observations: “yes they’re on a classic population expansion, resource depletion, greenhouse gas emission/climate collapse curve. We’ve seen it hundreds of times already. They won’t even have a planetary civilization in another 50 years. Let’s just move on.”

  • Gary Wilson April 23, 2019, 12:44

    Actually I’m optimistic about our chances. We’re having solar panels installed this summer. Thirty panels will produce about 10.3 kW of power a year. That will be enough to power the house and either feed energy into the grid or provide part of the power for an electric car. Technology can be wonderful. It’s time to catch up to Europe.

    • Triffin April 23, 2019, 18:23

      Gary ..

      Would the same dollar investment that you are about to make
      in solar panels provide a better return were you to invest
      in a portfolio of dividend paying utility companies and allocating
      the resulting dividend stream to your electric bill ??

      • Alex Tolley April 24, 2019, 22:11

        I think Gary’s response is the better way of thinking about this. Do things that benefit yourself AND the community, rather than just yourself. The financialization of our society has distorted our values, putting discounted cash flows as the supreme metric for making choices. We are well past time that our biosphere can be treated like an exploitable commons.

        As for that utility portfolio, I hope you didn’t include PG&E. ;)

  • Gary Wilson April 24, 2019, 13:03

    Hi Triffin. Thank you for the thoughtfulness of your comment. Part of the reason we are putting in solar panels is to make a statement in the neighborhood that things need to change. We also intend to convert to an electric car as soon as we can afford it. We are also pulling our investments out of our current bank because it has no green investment portfolio. In fact we have learned it is one of the worst banks in North America for continuing to fund oil development and expansion. Those days must come to an end. The future must be different if we are to have a long term future.

  • ljk April 25, 2019, 9:01

    In other China space news, they keep on exploring the lunar farside:


    A radio astronomy experiment hitching a ride on one of the communication satellites that keeps Earth in touch with China’s lunar farside explorers has returned its first results:


    Their test manned Mars base in the Gobi Desert is open for business:


    China plans on the following space missions through the next decade – A new space station, a lunar sample return mission, and a manned lunar base in the south polar region of the Moon:


    • Alex Tolley April 25, 2019, 12:44

      A moon base in a decade is impressive. Is the location to investigate water resources for extraction? No wonder NASA is pushing up their timeline so aggressively. I would happily see any nation set up such a base, rather than just make plans and then discard them.

      • ljk May 20, 2019, 11:42

        I would guess that water extraction for a lunar base is one big reason, since so much water ice is concentrated there. And they want to set up shop first.

        America is finally getting serious about a manned lunar base as well, but I will hold judgment until the first actual missions are being launched to the Moon. We have been given false promises too many times before.

  • Gary Wilson April 25, 2019, 13:15

    It will be interesting to see how much of the Chinese plan comes to fruition and whether they can keep to their planned schedule. I’m particularly interested in their manned program. If they succeed and put a manned base on the moon will it change the U.S. approach or timelines? I’m not a big fan of Jim Bridenstine. I see him as more of a public relations man than a true director of NASA. I hope I’m wrong but the U.S. manned effort seems to run through Spacex and Elon Musk now more than NASA.

    • ljk April 26, 2019, 9:10

      Jim Bridenstine has potential, but to be honest I haven’t seen a really good and effective NASA Administrator since James Webb. Too bad he has his name attached on a huge telescope project that is way over budget and years behind schedule. This is the man who got us to the Moon before the 1960s had ended.

  • ljk April 26, 2019, 9:23

    What can we learn from a failed return to the Moon?

    Casey Dreier • April 26, 2019

    Thirty years ago, President George H.W. Bush announced an ambitious program to return humans to the Moon. It failed. Today the Trump Administration wants the same thing. Can a failed lunar return effort help this one succeed?

    Full article here:


    Lesson 1: Minimize sticker shock

    Let’s be honest: anything sounds expensive when added up over thirty years. The National Parks Service, a wonderful organization that manages national parks and other monuments, is not a large part of the budget each year. Yet over the next three decades, it will spend roughly $100 billion. That’s just for parks! Space exploration costs more. That doesn’t mean it’s expensive, but lacking context it can certainly sound expensive. The United States regularly spends much more on many other programs. The Department of Defense, for example, will spend at least $21 trillion (yes, trillion) over the same timeframe, and has grown by tens of billions of dollars over the past few years with little public debate or notice. Space is cheap, by comparison.

    But that message isn’t enough. NASA’s infamous “90-Day Study,” which outlined its exploration ambitions for SEI in a 30-year time frame, estimated the program would cost between $400 and $500 billion (or close to a trillion of today’s dollars). Even though these initial studies were never formally proposed by the White House, SEI was forever laden with a politically laughable half-trillion-dollar price tag.

    Mars Wars: The Rise and Fall of the Space Exploration Initiative (SEI):


  • ljk May 20, 2019, 11:58

    China’s farside lunar lander may have found pieces of the Moon’s mantle:


    The little lunar comsat that made talking to the farside of the Moon possible will be ending its mission in July…