Expert Blog

Asteroid 2013 TX68

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Scientists from NASA’s Center for Near-Earth Object Studies at the Jet Propulsion Laboratory in Pasadena CA announced in February that a thirty meter sized near-Earth asteroid, tagged 2013 TX68, would pass safety by the Earth on March 8 of this year at a likely distance of 5 million kilometers, or about thirteen times the distance between the Earth and Moon. Their earlier, initial analysis suggested an Earth close approach on March 5 of this year with a remote (one in 250 million) Earth impact possibility in September of next year. This preliminary analysis was later revised to suggest a not-so- close Earth approach on March 8th. Asteroid 2013 TX68 was not observed during this early March Earth approach, but even so, there is no possibility of an Earth collision either in September of next year or at any time in the next one hundred years.

Why was the Earth close approach date advanced by three days, why wasn’t this asteroid observed during this recent close approach, and how can we be sure that this object poses no threat for more than 100 years?

The NASA-funded Catalina Sky Survey operating near Tucson Arizona discovered near-Earth asteroid 2013 TX68 on October 6, 2013. After only three days of tracking, the asteroid passed into the daylight sky and was then unobservable. By the time it went back into the night sky, it was too faint to be observed. With only three days of positional information, the asteroid’s position in its path around the sun could not be pinned down as precisely as it can with other asteroids. Its path was fairly well determined – but not its position along its path. More observations were needed. Think of a major league baseball outfielder trying to catch a high fly ball. When the baseball is first hit, our intrepid outfielder only knows it’s a high fly ball. He doesn’t know just where to move to get under it for the catch. As he watches the fly ball, he gets more and more information on the ball’s trajectory, he gets a better and better idea as to where the ball is headed, and he adjusts his field position accordingly.

This graphic depicts the orbit of asteroid 2013 TX68. The asteroid will fly by Earth on March 8. The asteroid poses no threat to Earth during this flyby or in the foreseeable future. Image credit: NASA/JPL-Caltech Image credit: NASA/JPL-Caltech
This graphic depicts the orbit of asteroid 2013 TX68. The asteroid will fly by Earth on March 8. The asteroid poses no threat to Earth during this flyby or in the foreseeable future. Image credit: NASA/JPL-Caltech Image credit: NASA/JPL-Caltech

The same is true for our asteroid orbit computers. When a few, pre-discovery positional observations of 2013 TX68 were located in the archives of the NASA-supported Pan-STARRS telescope in Hawaii, this additional information allowed for an improved knowledge of the asteroid’s trajectory – and an improved prediction for when the object would sail safely past the Earth on March 8th.

As noted, the asteroid’s path around the sun is relatively well known but its position on its path is much less well known. Think of a model train running around its oval track about a Christmas tree. If we’re out of the room, we don’t really know where the train is on its track but we do know where the track is so we’re not worried about the train running into the presents under the Christmas tree. The same is true for our asteroid’s orbit about the sun. Without additional positional observations, we may not know exactly where the asteroid is in its orbit, and hence where to look for it in the sky during its Earth approach on March 8, but we do know its orbital position and orbital track around the sun well enough to rule out any Earth impacts for the next 100 years.

Before the March 8th passage by the Earth, a misleading press release issued by the Slooh group of astronomers, announced that the facts for this asteroid’s passage by the Earth kept changing, JPL was unable to pin down its orbit and the Slooh group would use their robotic telescopes in an attempt to rediscover it. These folks need to understand that asteroid locations are always given as a range of possible positions with a most likely case somewhere in the middle. Any asteroid observed for only 3 days will have a wide range of possible positions 3 years later. When more observations became available for this asteroid, JPL scientists improved its orbit and narrowed the range. That’s the way the orbit improvement process works: the facts did not keep changing; as the Slooh astronomers alleged, they only led to more precise predictions. The fact that the nominal close approach distance and time changed is not inconsistent with the earlier report. Moreover, the asteroid’s position uncertainty along its orbital path during the March 8 Earth flyby was tens of degrees in extent making the Slooh astronomers attempt to observe the asteroid all but impossible. This type of information, for any asteroid at any time, is freely available to anyone who choses to become familiar with JPL’s websites, neo.jpl.nasa.gov and ssd.jpl.nasa.gov.

Let’s hope the information on these websites will be utilized before misleading statements are made about the next near-Earth object that flies past the Earth.

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Event Reports

Asteroid Day 2016 in Japan, Event Report.

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This event report was submitted by Makoto Yoshikawa (an Asteroid Day Expert) who ran several events across Japan as part of Asteroid Day 2016. You can read the original report, here.

=== The importance of Hayabusa and Hayabusa2 from the point of spaceguard ===

June 30th is Asteroid Day, which is a global awareness campaign for the hazard caused by asteroid collision to Earth. June 30th is the anniversary of the Tunguska event in Siberia on June 30, 1908. Mr. Grigorij Richters, one of the organizers of Asteroid Day, asked to JAXA to do something related to Asteroid Day. This is the trigger for the event reported here.

Hayabusa2 Project holds “Talk Live”, a kind of talk show, once in two months. We present various issues related to Hayabusa2 project. On June 12, 2016, we held the third Talk Live at Sagamihara City Museum. On the same day, we also had some events that celebrated the Earth return of Hayabusa, which was on June 13, 2010. Therefore, the main topic of the Talk Live on this day was set to Spaceguard (Planetary Defense), especially the role of Hayabusa and Hayabusa2 from the point of Spaceguard.

About 180 people came to the Talk Live (Fig.1). At first, I explain why we took spaceguard as the topic of today’s Talk Live, and then I presented many things related spaceguard, such as, recent impacts to the Earth, NEOs (Near Earth Objects), observations, orbits, mitigations, etc. I also explained the reason why Hayabusa and Hayabusa2 are important for spaceguard. You can see the video of this Talk Live in YouTube (https://youtu.be/BA1rEkmV4fw), although the talk is in Japanese.

Fig.1 Hayabusa2 Talk Live on June 12, 2016 at Sagamihara City Museum
Fig.1 Hayabusa2 Talk Live on June 12, 2016 at Sagamihara City Museum

In this report, I quickly summarize about the role of Hayabusa and Hayabusa2 in the context of spaceguard or planetary defense.

  • Hayabusa

Hayabusa, which was launched in 2003 and returned to Earth in 2010, was the world-fist sample return mission from an asteroid. The target asteroid is (25143) Itokawa, a small S-type asteroid (Fig.2). Itokawa is one of the NEOs. NEAR Shoemaker spacecraft was first to rendezvous with an NEO, Eros. Eros is about 38km in the length and it is not supposed that such a large NEO will collide to Earth in the near future. However, the size of Itokawa is just about 500m, and such object is what we must consider for the planetary defense.

Fig.2 Asteroid Itokawa
Fig.2 Asteroid Itokawa

After the exploration of Hayabusa, we concluded that the structure of Itokawa was a rubble pile (Fig.3), not the one single block of mass. We came to this conclusion not only from its surface feature with numerous boulders but also its density. The estimated density of Itokawa is about 1.9 g/cm3, while the density of the surface material of Itokawa, that is the ordinary chondrite, is about 3.2 g/cm3. If we assume that whole body of Itokawa consists of ordinary chondrite, then the macro-porosity is about 40%. Form this fact, we concluded that Itokawa has the rubble pile structure. This conclusion is very interesting for planetary science, and also it is very important information when we try to deflect an Earth-colliding asteroid like Itokawa.

Fig.3 Rubble pile structure of Itokawa
Fig.3 Rubble pile structure of Itokawa

Another interesting attempt for spaceguard in Hayabusa mission is to estimate the landing position of the reentry capsule on Earth. Of course, the landing position was estimated precisely by the radio navigation. However, assuming that Hayabusa was an asteroid that moved along the collision trajectory to Earth, we tried to estimate the landing (or colliding) position by optical observations. Optical observations by the ground-based telescopes were successful in the observatories of Tenaga, Mt. Lemon, Subaru, and CFHT. We got 23 data 10 to 8 hours before the landing. Using only these optical data without the information from the radio navigation, we estimated the landing position of the reentry capsule. The result was that the landing position was estimated with the error of about 560km (Fig.4).

Fig.4 Estimated the landing area of the reentry capsule by using only the optical observation data. The size of this estimated area is about 560km. (Cradited by T. Yamaguchi & M. Yoshikawa)
Fig.4 Estimated the landing area of the reentry capsule by using only the optical observation data. The size of this estimated area is about 560km. (Cradited by T. Yamaguchi & M. Yoshikawa)
  • Hayabusa2

Now let’s move on to Hayabusa2. Hayabusa2 is also an asteroid sample return mission. It was launched on December 3, 2014, and now it is on the way to the target asteroid (162173) Ryugu. Hayabusa2 will arrive at Ryugu in June – July 2018, and return to the Earth at the end of 2020 (Fig.5).

Fig.5 Mission scenario of Hayabusa2
Fig.5 Mission scenario of Hayabusa2

From the point of Spaceguard, the most important role of Hayabusa2 is to reveal the nature of small C-type asteroid. Asteroid Ryugu was selected because it is C-type. The science purpose of Hayabusa2 is to study organic matters and water, which may be in the surface material of Ryugu. The size of Ryugu is estimated as 900m and it approach Earth closely (Fig.6). Therefore, Ryugu is another realistic candidate that will collide to Earth. Is the structure a rubble pile again like Itokawa? Hayabusa2 will give us the answer to this question.

Fig.6 Asteroid Ryugu
Fig.6 Asteroid Ryugu

Another interesting attempt of Hayabusa2 is its impactor. Hayabusa2 has an impactor on board, and it will be released near the surface of Ryugu. The impactor will explode a few hundred meters above the surface of Ryugu and a lump of copper (2kg) will hit the surface at the speed of 2 km/s. Then we can create a small crater there. The purpose of this experiment is to get the sub-surface material. From the point of spaceguard, this is the exactly the same idea of the kinetic impactor. Of course the impactor of Hayabusa2 is quite small so we cannot change the orbit of asteroids. But I think this is a very interesting experiment for spaceguard, too.

In fact, in the early planning phase of Hayabusa2, we were discussing to have a much larger impactor. It was one spacecraft. Our idea was that Hayabusa2 and the impactor spacecraft would launched at the same time by the same launcher, and the impactor spacecraft would hit Ryugu after Hayabusa2 would observe it and get the sample from it (Fig.7). This is the similar idea that is now discussed as AIDA mission by ESA and NASA. In this case, we cannot change the orbit of Ryugu largely because Ryugu is too large to change its orbit by such a small spacecraft. But our analysis shows that such impactor spacecraft will be effective to change the orbit of asteroids in the size of 60 m. This is the similar size of the body that impacted at Tunguska in 1908.

Fig.7 Scenario of Hayabusa2 with an impactor spacecraft This scenario was studied in the early phase of the planning Hayabusa2.
Fig.7 Scenario of Hayabusa2 with an impactor spacecraft This scenario was studied in the early phase of the planning Hayabusa2.

The principal purposes of Hayabusa and Hayabusa2 are to develop technologies for sample return from small NEOs and to study the origin and evolution of the solar system bodies and the life. In addition to these, Hayabusa and Hayabusa2 will contribute to the activities of the spaceguard.

Makoto Yoshikawa, Hayabsua2 Talk Live Coordinator

 

 

 

 

 

 

 

 

Makoto Yoshikawa, Hayabsua2 Talk Live Coordinator
June 28, 2016

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Article

51 DEGREES NORTH Live on ASTEROIDDAY.org along with worldwide LIVE feeds

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51 Degrees North is now on the website homepage for free until midday July 1st. Check it out now!

51 Degrees North – Watch the full film for free. 24 hours only from Asteroid Day on Vimeo.

In support of Asteroid Day events worldwide the Asteroid Day homepage will host 51 Degrees North for free for 24 hours and provide you with live coverage about Asteroid Day worldwide. This live coverage feed will be available on our website, promoting all the many  events happening around the world. We will be updating our live stream with event details and retweeting photos and videos of local events and asteroid-related content. So, don’t forget to take pictures and videos and share them with us using #AsteroidDay

Or email photos, videos, and descriptions of your event to events@asteroidday.org for promotion and mentions on the website.

 

 

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