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Ultima Thule Flyby Approaches

Despite the various governmental breakdowns attendant to the event, the New Horizons flyby of Ultima Thule is happening as scheduled, the laws of physics having their own inevitability. Fortunately, NASA TV and numerous social media outlets are operational despite the partial shutdown, and you’ll want to keep an eye on the schedule of televised events as well as the New Horizons website and the Johns Hopkins Applied Physics Laboratory YouTube channel.

Image: New Horizons’ path through the solar system. The green segment shows where New Horizons has traveled since launch; the red indicates the spacecraft’s future path. The yellow names denote the Kuiper Belt objects New Horizons has observed or will observe from a long distance. (NASA/JHUAPL/SwRI).

We’re close enough now, with flyby scheduled for 0533 UTC on January 1, that the mission’s navigation team has been tightening up its estimates of Ultima Thule’s position relative to the spacecraft, key information when it comes to the timing and orientation of New Horizons’ observations. Raw images from the encounter will be available here. Bear in mind how tiny this object is — in the range of 20 to 30 kilometers across — so that we have yet to learn much about its shape and composition, though we’ve already found that it has no detectable light curve.

On the latter point, mission principal investigator Alan Stern (SwRI):

“It’s really a puzzle. I call this Ultima’s first puzzle – why does it have such a tiny light curve that we can’t even detect it? I expect the detailed flyby images coming soon to give us many more mysteries, but I did not expect this, and so soon.”

Thus the mission proceeds in this last 24 hours before flyby with grayscale, color, near-infrared and ultraviolet observations, along with longer-exposure imaging to look for objects like rings or moonlets around Ultima. Closest approach is to be 3,500 kilometers at a speed of 14.43 kilometers per second. JHU/APL is reporting that the pixel sizes of the best expected color and grayscale images and infrared spectra will be 330 meters, 140 meters and 1.8 kilometers, respectively, with possible images at 33-meter grayscale resolution depending on the pointing accuracy of LORRI, the Long Range Reconnaissance Imager.

Image: New Horizons’ cameras, imaging spectrometers and radio science experiment are the busiest members of the payload during close approach operations. New Horizons will send high-priority images and data back to Earth in the days surrounding closest approach; placed among the data returns is a status check – a “phone home signal” from the spacecraft, indicating its condition. That signal will need just over 6 hours, traveling at light speed, to reach Earth. (NASA/JHUAPL/SwRI).

Post flyby, New Horizons will turn its ultraviolet instrument back toward the Sun to scan for UV absorption by any gases the object may be releasing, while simultaneously renewing the search for rings. Scant hours after the flyby, New Horizons will report back on the success of the encounter, after which the downlinking of approximately 7 gigabytes of data can begin. The entire downlink process, as at Pluto/Charon, is lengthy, requiring about 20 months to complete.

Let’s keep in mind that, assuming all goes well at Ultima Thule, we still have a working mission in the Kuiper Belt, one with the potential for another KBO flyby, and if nothing else, continuing study of the region through April of 2021, when the currently funded extended mission ends (a second Kuiper Belt extended mission is to be proposed to NASA in 2020). The Ultima Thule data return period will be marked by continuing observation of more distant KBOs even as New Horizons uses its plasma and dust sensors to study charged-particle radiation and dust in the Kuiper Belt while mapping interplanetary hydrogen gas produced by the solar wind.

So let’s get this done, and here’s hoping for a successful flyby and continued exploration ahead! It will be mid-afternoon UTC on January 1 (mid-morning Eastern US time) when we get the first update on the spacecraft’s condition, with science data beginning to arrive at 2015 UTC, and a first 100 pixel-across image (and more science data coming in) on January 2 at 0155 UTC. The best imagery is going to take time to be released, perhaps becoming available by the end of February. We’ll be talking about Ultima Thule a good deal between now and then.


Comments on this entry are closed.

  • Charlie December 31, 2018, 12:02

    What’s so often forgotten about in the excitement of all these pre-encounter path maneuvers to get the safest and closest approach to any of these objects while they are flying by at speeds greater than that of a bullet, is the fact that careful calculations MUST BE DONE on the speed in which the photographic platform must be determined and calculated to permit a reasonably sharp image of what you’re trying to image.
    I hardly need to remind everybody that this is due to the finite speed of light and the very short, short timeframe you have available to bring the camera to focus so as to prevent smearing and distortion of the image within the range of your optics. I’d assume that the same considerations apply to the non-photographic instrumentation as well. Certainly something to marvel over.

    • Martin Andersen December 31, 2018, 16:01

      It takes the spacecraft 2 seconds to pass the object , that’s crazy..

  • Robert December 31, 2018, 12:30

    Why is the data rate so slow? Twenty months for only 7GB is less than 150 bytes per second which strikes me as absurdly slow for spacecraft which costs 700 million dollars.

    • Antonio December 31, 2018, 13:48

      Low power, small antenna, long distance. See:


    • Randy Chung December 31, 2018, 16:50

      New Horizons is now about 44.25 AU or 4.1 billion miles away from the Earth. Its transmit power is 12 watts per amplifier — it has two, but might only have enough power from the RTG to run one.

      So let’s do a very rough comparison of a 12 watt amplifier 4 billion miles away with a 4G cellular amplifier at 20 miles away. Theoretically, your 4G cellphone might be able to download at 50 Mbps from the base station, which might transmit at 10 watts or so. This seems optimistic, especially at 20 miles distance, but let’s just use that.

      So 4.1 billion miles divided by 20 miles is about 200 million. If the data rate scaled linearly with distance (of course, it doesn’t) then you would expect the 50 Mpbs cellphone data rate to be divided by 200 million, or go down to a quarter bit per second. The data rate actually scales with the *square* of the distance, so the data rate should be reduced by a factor of another 200 million. You can make up some of the difference by using the big 70 meter antennas in the Deep Space Network, and the 2 meter New Horizons antenna is bigger than a cellphone tower antenna, but both together might only get you another factor of 10,000.

      So you would expect New Horizons to only be able to transmit at much less than 1 bps if it used cellphone level technology. It amazes me that it is able to reach anywhere near 2000 bps. And since this is also an interstellar website, it baffles me as to how we’ll communicate at light year distances, even if we use lasers.

      • Andrei December 31, 2018, 18:45

        Yes it ‘baffle’ me too, so much I do not understand how anyone can imagine a micrometeorite or even just a chip to be able to send any useful information over interstellar diastances – if one such is ever sent on one of those proposed laser powered sails.

        I am looking forward to this encounter, I hope they given priority to some image so that we’ll get to see something by January 2.

        My prediction – it will look a bit that one of the comet nucleus we’ve studied closely. Some objects tumbling nearby after a collision, this to explain the lack of a light-curve. Only limited heated from collisions and some craters and tars / organics.

      • Michael C. Fidler December 31, 2018, 21:56

        I can remember back in 1980 the first modem I saw was at the Nellis Tonopah radar range and had a speed of 300 bits per second. Lasers with the rate we are developing quantum systems should be able to go over light years with very little diffraction. The beam could almost be as bright as if shot from our moon, the only problem is with how much interstellar medium would attenuate the light. Then there is the question of how quantum entanglement might be used to either have perfect reception or even instantaneous FTL reception!!!

        • AlexT January 2, 2019, 4:37

          Then there is the question of how quantum entanglement might be used to either have perfect reception or even instantaneous FTL reception!!!
          There is one little problem – quantum entanglement cannot be used for FTL communication…

      • Alex Tolley December 31, 2018, 22:35

        I remember when data was transmitted over land lines at less than 300 bps. That classic acoustically perceptible sound.

      • Michael January 1, 2019, 3:30

        With the starchip they are thinking of using the gravifocal phenomena to focus the signals back to earth. The power and loss rates become very small allowing effective transmissions over vast distances.

        • David January 1, 2019, 11:52


      • Robert January 1, 2019, 12:54

        Thanks for the detailed answer and other responses. I note from the NASA press kit the following information;

        New Horizons’ X-band communications system is the spacecraft’s link to Earth, returning science data, exchanging commands and status information, and allowing for precise radiometric tracking through NASA’s Deep Space Network of antenna stations.
        The system includes two broad-beam, low-gain antennas on opposite sides of the spacecraft for near-Earth communications: a 30-centimeter (12-inch) diameter medium-gain dish antenna and a large, 2.1-meter (83-inch) diameter high-gain dish antenna. The antenna assembly on the spacecraft’s top deck consists of the high, medium, and forward low-gain antennas; this stacked design provides a clear field of view for the low-gain antenna and structural support for the high and medium-gain dishes. Operators aim the antennas by turning the spacecraft toward Earth. The high-gain beam is only 0.3 degrees wide, so it must point directly at Earth. The medium-gain beam is wider (14 degrees), so it is used in conditions when the pointing might not be as accurate. All antennas have Right Hand Circular and Left Hand Circular polarization feeds.

        “Data rates will depend on spacecraft distance, the power used to send the data and the size of the antenna on the ground. For most of the mission, New Horizons will use its high-gain antenna to exchange data with the Deep Space Network’s largest antennas, 70 meters across. Even then, because New Horizons will be more than 3 billion miles from Earth and radio signals will take more than four hours to reach the spacecraft, it can send information at about 700 bits per second. It will take nine months to send the full set of Pluto encounter science data back to Earth.”

        The press kit pdf is here;

        Thanks again for the responses.

  • Rob Flores December 31, 2018, 12:45

    I predict. essentially a glob of hydrocarbons resembling tar in
    aspect and behavior, though just a mimic of tar. Various longer chain (6-at least) hydrocarbons in a cold vacuum will be the actual surface composition.

  • Ashley Baldwin December 31, 2018, 14:18

    I’m just waiting to see how long it takes Alan Stern to declare it a planet.

    • Michael C. Fidler December 31, 2018, 21:35

      Or a tar covered light-sail!

    • Rob Flores December 31, 2018, 21:44

      Why do I picture a certain duck, a flag
      and a earth ship, claiming it. Bonus: It can disintegrate too.

  • Bruce D. Mayfield December 31, 2018, 18:31

    On the issue of the unexpectedly flat light curve seen on approach, it occurred to me that there would be no light variation if it doesn’t rotate, or if has a very very slow rotation rate. I know everything is expected to have rotation, but the light curve would look this way if it always kept one side pointed toward the sun and inner solar system, like tidally locked moons and exoplanets do. But that’s an absurdly long way from Sol for it to have tidally locked, isn’t it?

    Apparently, approximately nil rotation is deemed so unlikely an explanation that no professional has suggested it. But “the universe is not only stranger than we imagine, it’s stranger than we CAN imagine”, if I’ve got the quote right. So if I was a gambler I’d take the long odds. I predict very slow rotation as at least part of the explanation for the flat light curve.

  • Andrew Palfreyman December 31, 2018, 20:56
  • Ashley Baldwin January 1, 2019, 11:49

    Well New Horizons has phoned home. Good. Now let’s hope it has managed to capture some decent pictures as it raced past its target. Shouldn’t have to wait too long for the first low resolution images .

  • David January 1, 2019, 11:57

    NASA TV has been on despite shutdown …..after UT they can go back to Earth Views but it has been great coverage. Just watched the signal arrival They have the data. Press Conf in half hour. Last night it was by far the best countdown show especially with Brian May.There were excellant presentations on the mission geology and the outer solar system.