Enjoying EarthSky? Subscribe.

211,905 subscribers and counting ...

Update: 2015 TB145 likely a dead comet

Last week heralded as largest known asteroid to pass Earth until 2027. Swept within 1.3 times the moon’s distance on October 31. Now thought to be a comet!

This image of asteroid 2015 TB145, a dead comet, was generated using radar data collected by the National Science Foundation's 1,000-foot (305-meter) Arecibo Observatory in Puerto Rico. The radar image was taken on Oct. 30, 2015, and the image resolution is 25 feet (7.5 meters) per pixel. Image credit: NAIC-Arecibo/NSF

This image of asteroid 2015 TB145, a dead comet, was generated using radar data collected by the National Science Foundation’s 1,000-foot (305-meter) Arecibo Observatory in Puerto Rico. The radar image was taken on Oct. 30, 2015, and the image resolution is 25 feet (7.5 meters) per pixel. Image via NAIC-Arecibo/NSF.

UPDATE OCTOBER 31, 2015 The large space object that is zipping past Earth this Halloween is most likely a dead comet that, fittingly, bears an eerie resemblance to a skull. Scientists observing asteroid 2015 TB145 with NASA’s Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii, have determined that the celestial object is more than likely a dead comet that has shed its volatiles after numerous passes around the sun. The newly found object – first thought to be an asteroid and given the asteroid name 2015 TB145 – is safely passing Earth on October 31, 2015, according to clocks in North America. This object – found on October 10 – will fly past Earth at a safe distance, or about 1.3 times the moon’s distance. Closest approach to Earth will be October 31 at 1 p.m. EDT (1700 UTC). Translate to your time zone here. Follow the links below for more.

Halloween “asteroid” is most likely a dead comet

Best time to view the asteroid was the night of October 30

How close will asteroid 2015 TB145 come to the Earth and moon?

How big is it?

When and how did scientists discover asteroid 2015 TB145?

How will scientists observe it?

Similar close approaches of other asteroids

When will asteroid 2015 TB145 sweep near Earth again?

View larger. | This graphic depicts the orbit of asteroid 2015 TB145. Image via NASA/JPL-Caltech.

View larger. | This graphic depicts the orbit of object 2015 TB145, now thought to be a comet, not an asteroid. Image via NASA/JPL-Caltech.

2015 TB145 with NASA's Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii.

2015 TB145 with NASA’s Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii.

Halloween “asteroid” is most likely a dead comet. The large space rock that zipping past Earth this Halloween is most likely a dead comet that bears an eerie resemblance to a skull, NASA says. A story at JPL’s website late Friday reported:

Scientists observing asteroid 2015 TB145 with NASA’s Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii, have determined that the celestial object is more than likely a dead comet that has shed its volatiles after numerous passes around the sun.

The belated comet has also been observed by optical and radar observatories around the world, providing even more data, including our first close-up views of its surface. Asteroid 2015 TB145 will safely fly by our planet at just under 1.3 lunar distances, or about 302,000 miles (486,000 kilometers), on Halloween (Oct. 31) at 1 p.m. EDT (10 a.m. PDT, 1700 UTC).

The first radar images of the dead comet were generated by the National Science Foundation’s 305-meter (1,000-foot) Arecibo Observatory in Puerto Rico. The radar images from Arecibo indicate the object is spherical in shape and approximately 2,000 feet (600 meters) in diameter and completes a rotation about once every five hours.

Kelly Fast, IRTF program scientist at NASA Headquarters and acting program manager for NASA’s NEO Observations Program, said:

The IRTF data may indicate that the object might be a dead comet, but in the Arecibo images it appears to have donned a skull costume for its Halloween flyby.

The IRTF’s 3-meter (10 foot) telescope collected infrared data on the object. The data may finally put to rest the debate over whether 2015 TB145, with its unusual orbit, is an asteroid or is of cometary origin. Vishnu Reddy, a research scientist at the Planetary Science Institute, Tucson, Arizona, said:

We found that the object reflects about six percent of the light it receives from the sun.

That is similar to fresh asphalt, and while here on Earth we think that is pretty dark, it is brighter than a typical comet which reflects only 3 to 5 percent of the light. That suggests it could be cometary in origin — but as there is no coma evident, the conclusion is it is a dead comet.

View larger. |

View larger. | Radar images generated by the team at Arecibo.

Facing east from U.S. at 11:50 pm ET October 30, 2015 (late on Friday night). Illustration by Eddie Irizarry using Stellarium.

Facing east from U.S. at 11:50 pm ET October 30, 2015 (late on Friday night). Illustration by Eddie Irizarry using Stellarium.

Best time to view the asteroid was the night of October 30. Asteroid 2015 TB145 is not visible to the eye alone. Observers trying to glimpse the space rock using telescopes will have to look late at night of October 30, and before dawn on October 31.

At its brightest, the space rock is at an approximate magnitude of 10. For experienced observers, it should be easy to spot “slowly” moving across the field of stars, assuming you know when and where to look. On the night of October 30-31, the asteroid will be traveling across the well-known constellation of Orion. Because of its large size, advanced amateur astronomers might be able to see the movement of the asteroid in telescopes of 8″ in diameter or larger.

And, by the way, although the asteroid’s distance will make this moving object appear to move slowly, this speeding space rock is traveling at 78,000 miles (126,000 km) per hour!

More tips and charts for observers below:

Asteroid position at 11:20 ET (0320 UTC) on Octoner 30. If you have a computerized (Go To) telescope, point it to HIP 22845 or SAO 94201, a 4th magnitude star in Orion before 11:20 p.m. ET on October 30 (Friday night) and wait for the asteroid. The space rock will appear as a slowly moving ‘star’ passing very close to this actual fixed star at that time. This view shows a half degree field of view (about the size of a full moon). Alternatively, you can point your telescope to these coordinates: RA 04h 54m 53.755 s / DEC +10º 09' 02.60

Asteroid position at 11:20 ET (0320 UTC) on October 30. If you have a computerized (Go To) telescope, point it to HIP 22845 or SAO 94201, a 4th magnitude star in Orion before 11:20 p.m. ET Friday night, and wait for the asteroid. The space rock will appear as a slowly moving ‘star’ passing very close to this actual fixed star at that time. This view shows a half degree field of view (about the size of a full moon). Alternatively, you can point your telescope to these coordinates: RA 04h 54m 53.755 s / DEC +10º 09′ 02.60″. Illustration by Eddie Irizarry using Stellarium.

Asteroid position at 12:05 a.m. ET (0405 UTC) on October 31.  Have a Go To computerized telescope? Point it to HIP 23035 or SAO 94225, a 7th magnitude star in Orion. At 12:05 a.m. ET on October 31 (Saturday morning), the space rock passes close to this star. The asteroid will appear as a slowly moving ‘star’ passing close to this star. This illustration shows a half degree field of view (about the size of a full moon). Alternatively, you can point your telescope to these coordinates: RA 4h 57m 13.1s / DEC +10º 48' 35.5

Asteroid position at 12:05 a.m. ET (0405 UTC) on October 31. Point a Go To computerized telescope to HIP 23035 or SAO 94225, a 7th magnitude star in Orion. On Saturday morning at 12:05 a.m. ET, the space rock passes close to this star. The asteroid will appear as a slowly moving ‘star’ passing close to this star. This illustration shows a half degree field of view (about the size of a full moon). Alternatively, you can point your telescope to these coordinates: RA 4h 57m 13.1s / DEC +10º 48′ 35.5″. Illustration by Eddie Irizarry using Stellarium.

1. Although the asteroid may be visible with smaller telescopes, its motion should be easier to see by advanced amateur astronomers using an 8″ or bigger diameter telescope.

2. Note that the asteroid’s nearness to Earth at the time of closest approach might cause a parallax effect. That means the space rock’s apparent nearness on our sky’s dome to a fixed star might differ slightly, as seen from different locations across Earth. Thus, if you don’t see the asteroid at the expected time, scan one more field of view up and down from your reference star, that is, the star you are waiting to see the asteroid to pass by.

3. A wide-angle eyepiece can be initially used for the asteroid search; however a medium power eyepiece such as a 17mm will show better the motion of this asteroid.

4. Remember that you will be looking for an apparent “moving star” slowly passing in front of actual fixed stars visible in a telescope. If you are using an 8″ telescope with a 17mm eyepiece, at around 2:20 a.m. CT on Saturday, October 31 the asteroid’s motion should cover the entire field of view in about 7 minutes. A few hours later it will appear to move faster because the asteroid will be getting closer to us.

5. Because the moon’s presence will illuminate your observing session, it is a good idea to cover your head with dark clothes or a black t-shirt while observing. This will let you have a better view of only what is visible though the eyepiece of the telescope and avoid distractions.

Asteroid position at 1:30 a.m. ET (5:30 UTC). If you have a computerized (Go To) telescope, point it to HIP 23382 or SAO 94272, a 7 magnitude star in Orion before 1:30 a.m. ET on October 31 (Saturday morning) and wait for the asteroid. The space rock will appear as a slowly moving ‘star’ passing close to this actual fixed star at that time. This view shows a half degree field of view (about the size of a full moon). Alternatively, you can point your telescope to these coordinates: RA 05h 01m 36.8 s / DEC +12º 20' 25.4

Asteroid position at 1:30 a.m. ET (5:30 UTC). Point a Go To computerized telescope to HIP 23382 or SAO 94272, a 7 magnitude star in Orion before 1:30 a.m. ET Saturday morning Saturday morning and wait for the asteroid. Field of view half a degree. Alternatively, you can point your telescope to these coordinates: RA 05h 01m 36.8 s / DEC +12º 20′ 25.4″. Illustration by Eddie Irizarry using Stellarium.

Asteroid position at 2:55 a.m. ET (655 UTC). Have a Go To computerized telescope? Point it to HIP 23786 or SAO 94322, a 7th magnitude star in Orion. At 2:55 a.m. ET on October 31 (Saturday morning), the space rock passes very close to this star. The asteroid will appear as a slowly moving ‘star’ passing close to this star. This illustration shows a half degree field of view (about the size of a full moon). Alternatively, you can point your telescope to these coordinates: RA 5h 06m 42.5s / DEC +14º 26' 42.7

Asteroid position at 2:55 a.m. ET (655 UTC). Point a Go To computerized telescope to HIP 23786 or SAO 94322, a 7th magnitude star in Orion. At 2:55 a.m. ET on Saturday morning, the space rock passes very close to this star. The asteroid will appear as a slowly moving ‘star’ passing close to this star. View of view half a degree. Alternatively, you can point your telescope to these coordinates: RA 5h 06m 42.5s / DEC +14º 26′ 42.7″. Illustration by Eddie Irizarry using Stellarium.

Asteroid position at 3:20 a.m. ET (7:20 UTC). If you have a computerized (Go To) telescope, point it to HIP 23939 or SAO 94344, an 8 magnitude star in Orion. At 3:20 a.m. ET on October 31 (Saturday morning), the space rock passes very close to this star. The asteroid will appear as a slowly moving ‘star’ passing close to this star. This illustration shows a half degree field of view (about the size of a full moon). Alternatively, you can point your telescope to these coordinates: RA 5h 8m 42.3s / DEC +15º 06' 13.6

Asteroid position at 3:20 a.m. ET (7:20 UTC). Point a Go To computerized telescope to HIP 23939 or SAO 94344, an 8 magnitude star in Orion. At 3:20 a.m. ET on October 31 (Saturday morning), the space rock passes very close to this star. The asteroid will appear as a slowly moving ‘star’ passing close to this star. This illustration shows a half degree field of view (about the size of a full moon). Alternatively, you can point your telescope to these coordinates: RA 5h 8m 42.3s / DEC +15º 06′ 13.6″. Illustration by Eddie Irizarry using Stellarium.

Asteroid position at 3:35 ET (0735 UTC). Point to 15 Orionis (HIP 24010 or SAO 94359) a naked-eye star with a magnitude of 4.8 in Orion. At 3:35 a.m. ET on October 31 (Saturday morning), the space rock passes close to this star. The asteroid will appear as a slowly moving ‘star’ passing very close to this star. By this time the asteroid should appear to move faster because it will be closer to Earth than earlier on the night of October 30. This illustration shows a half degree field of view (about the size of a full moon). Alternatively, you can point your telescope to these coordinates: RA 05h 09m 42.0s / DEC +15º 35' 49.8

Asteroid position at 3:35 ET (0735 UTC). Point to 15 Orionis (HIP 24010 or SAO 94359) a naked-eye star with a magnitude of 4.8 in Orion. At 3:35 a.m. ET Saturday morning, the space rock passes close to this star. The asteroid will appear as a slowly moving ‘star’ passing very close to this star. By this time the asteroid should appear to move faster because it will be closer to Earth than earlier on the night of October 30. Field of view half a degree. Alternatively, you can point your telescope to these coordinates: RA 05h 09m 42.0s / DEC +15º 35′ 49.8″. Illustration by Eddie Irizarry using Stellarium.

Asteroid position at 3:50 a.m. ET (0750 UTC) If you have a computerized (Go To) telescope, point it to HIP 24197 or SAO 94377) a naked-eye star with a magnitude of 5 in Orion. At 3:50 a.m. ET on October 31 (Saturday morning), the space rock passes close to this star. The asteroid will appear as a slowly moving ‘star’ passing very close to this star. By this time the asteroid should appear to move faster because it will be closer to Earth than earlier on the night of October 30. This illustration shows a half degree field of view (about the size of a full moon). A pair of double stars visible in this area should confirm you are pointing at the correct direction. Alternatively, you can point your telescope to these coordinates: RA  05h 11m 41.6s / DEC +16º 02' 44.5

Asteroid position at 3:50 a.m. ET (0750 UTC) Point a Go To computerized telescope to HIP 24197 or SAO 94377) a naked-eye star with a magnitude of 5 in Orion. At 3:50 a.m. ET on October 31 (Saturday morning), the space rock passes close to this star. The asteroid will appear as a slowly moving ‘star’ passing very close to this star. By this time the asteroid should appear to move faster because it will be closer to Earth than earlier on the night of October 30. This illustration shows a half degree field of view (about the size of a full moon). A pair of double stars visible in this area should confirm you are pointing at the correct direction. Alternatively, you can point your telescope to these coordinates: RA 05h 11m 41.6s / DEC +16º 02′ 44.5″. Illustration by Eddie Irizarry using Stellarium.

How close will asteroid 2015 TB145 come to the Earth and moon? The huge asteroid will pass Earth at 310,000 miles (498,896 km) or 1.3 times the Earth-moon distance, which is a totally safe pass.

It’ll come closer to the moon than to Earth, only 180,000 miles (280,000 km) from the moon.

Paul Chodas, manager of the Center for Near Earth Object Studies at NASA’s Jet Propulsion Laboratory, Pasadena, California, said:

The trajectory of 2015 TB145 is well understood. At the point of closest approach, it will be no closer than about 300,000 miles – 480,000 kilometers or 1.3 lunar distances. Even though that is relatively close by celestial standards, it is expected to be fairly faint, so night-sky Earth observers would need at least a small telescope to view it.

How big is it? Scientists are continuing to estimate the size at 1,300 feet (400 meters) wide.

If the size is correct, the new found asteroid is 28 times bigger in diameter than the Chelyabinsk meteor that penetrated the atmosphere over Russia in February, 2013. An incoming asteroid’s potential to do damage on Earth depends on various factors, including its size, its angle of entry, and the point on Earth over which it enters the atmosphere. The shock wave from the 2013 Chelyabinsk meteor broke windows and did other damage to some 7,200 buildings in six Russian cities. Some 1,500 people were injured seriously enough to seek medical treatment, mainly from broken glass from windows.

When and how did scientists discover asteroid 2015 TB145? They first spotted it on October 10, 2015 with the Pan-STARRS I telescope in Hawaii.

Because it was discovered so recently, only three weeks before its closest encounter with Earth, it is fortunate that asteroid 2015 TB145 is passing at a safe distance.

It’s a reminder of a comment made by NASA Administrator Charles Bolden in March, 2013, while addressing the U.S. House Science, Space, and Technology Committee at a meeting to discuss the threat of incoming asteroids like the Chelyabinsk meteor, which had happened just a month earlier. Bolden was trying to emphasize the need for adequate U.S. funding for detecting and characterizing near-Earth objects, and diverting them if necessary, when he told the committee:

From the information we have, we don’t know of an asteroid that will threaten the population of the United States. But if it’s coming in three weeks … pray.

Asteroid 2015 TB145, too – a large asteroid, discovered so recently – is a reminder of how important it is to support and improve the asteroid detection programs, such as NASA’s Near-Earth Object program. It’s also important to continue scientific studies about what might be done if a dangerous asteroid is detected on a possible collision course with Earth.

Various space agencies are already working towards earlier asteroid detections, but more funding is always required.

NASA is also planning to catch an asteroid, move it closer to our moon’s orbit, and then send astronauts to study how we can change the space rock’s orbit.

Goldstone - near Barstow, California - is the largest tracking station in NASA's Deep Space Network, which is composed of three installations located at roughly 120-degree intervals around the globe (with one at Madrid, Spain, and another at Canberra, Australia) for a continuous view of space.

Goldstone – near Barstow, California – is the largest tracking station in NASA’s Deep Space Network, which is composed of three installations located at roughly 120-degree intervals around the globe (with one at Madrid, Spain, and another at Canberra, Australia) for a continuous view of space. Image via Land Use Data Base.

How will scientists observe asteroid 2015 TB145? NASA scientists said this week they are now tracking the upcoming Halloween flyby of this asteroid with several optical observatories and the radar capabilities of the agency’s Deep Space Network at Goldstone, California.

Lance Benner of the Jet Propulsion Laboratory in Pasadena, California, who leads NASA’s asteroid radar research program, said in a story at JPL’s website:

The close approach of 2015 TB145 at about 1.3 times the distance of the moon’s orbit, coupled with its size, suggests it will be one of the best asteroids for radar imaging we’ll see for several years. We … hope to see unprecedented levels of detail.

He added that this object might not be an asteroid at all, but instead “some type of comet.” Comets tend to have more elongated orbits than asteroids. They tend to be icy, rather than rocky or metallic, bodies. Benner said:

The asteroid’s orbit is very oblong with a high inclination to below the plane of the solar system. Such a unique orbit, along with its high encounter velocity – about 35 kilometers or 22 miles per second – raises the question of whether it may be some type of comet. If so, then this would be the first time that the Goldstone radar has imaged a comet from such a close distance.

Similar close approaches of other asteroids. NASA has said asteroid 2015 TB145 is the biggest known space rock to pass near Earth until 2027, when asteroid 1999 AN10 will safely pass by Earth:

According to the catalog of near-Earth objects (NEOs) kept by the Minor Planet Center, this is the closest currently known approach by an object this large until asteroid 1999 AN10, at about 2,600 feet (800 meters) in size, approaches at about 1 lunar distance (238,000 miles from Earth) in August 2027.

In January, 2015 another asteroid, BL86 came some 1.2 million km (745,000 miles) from our planet. The 325 meter (1,100 ft) was also seen moving across the stars though telescopes.

Since asteroid 2015 TB145 appears to be bigger, and will pass even closer, its movement may be easier to spot than was the motion of asteroid BL86.

When will asteroid 2015 TV145 sweep near Earth again? According to NASA, after this Halloween (October 31, 2015), the next sweep of the asteroid past Earth will be on November 10, 2018, but, at that time, the asteroid will be nearly 25 million miles (40 million km) away. A closer encounter will take place in the year 2152.

Artist's concept of a large asteroid passing Earth, via Shutterstock.

Artist’s concept of a large asteroid passing Earth, via Shutterstock.

Bottom line: Asteroid 2015 TB145 – largest known space rock to sweep near Earth until 2027 – will pass about 1.3 times the moon’s distance on October 31, 2015. This post contains information on the asteroid’s estimated size, its closest approach to the Earth and moon, tips for observing it with a telescope, how scientists intend to observe it, other close approaches of similarly sized asteroids, and more.

Eddie Irizarry

MORE ARTICLES