The Virtual Telescope Project, based in Rome, Italy, captured asteroid (99942) Apophis on March 2, 2021. The asteroid appears as a point – while the stars around it appear as stripes – because the telescope followed the asteroid’s movement . It moves through space relative to the Earth at a speed of 4.658 km / sec (2.894 miles / sec). Image via virtual telescope.
Astronomers this week focused their gaze on the asteroid Apophis as it flies closest to Earth before its extraordinarily short 2029 pass. It will get its closest on March 5 and 6, 2021, not particularly close this time, but still within range of terrestrial telescopes and radar. Apophis is a relatively large asteroid near Earth (nearly 400 meters wide). It caused a stir in 2004 when early observations suggested it could hit Earth as it sweeps by in 2029. A strike in 2029 was then ruled out, and Apophis is not expected to hit Earth in this century. But this asteroid is a frequent visitor to our part of space, and astronomers want to know more.
Asteroid Apophis will come closest to our planet on March 6, 2021 at 01:15 UTC (on March 5 at 8:15 pm EST; translate UTC to your time). At this pass for 2021, it comes within 10,471,577 miles (16,852,369 km). That’s about 44 times the distance from the moon, a very safe distance for this pass.
NASA’s Goldstone Deep Space Communications Complex in California has had the asteroid on its observation schedule since March 3, 2021, and plans to continue to observe it until March 14. Researchers at the Green Bank Telescope in West Virginia also began observing Apophis on March 3; Green Bank coordinates observations with Goldstone because using these two telescopes together makes the data sharper. Astronomers, of course, mourn the loss of the Arecibo telescope in Puerto Rico. On the street, it is said that Arecibo – known for its radar observations of asteroids – would have been the world’s best telescope to observe Apophis this year. However, Arecibo collapsed last fall, decommissioning the telescope. The International Asteroid Warning Network (IAWN) – with members in Europe, Asia and South and North America – serves as a clearinghouse for the 2021 campaign to observe Apophis. The coordinator is astronomer Vishnu Reddy, a planetary defense expert at the University of Arizona.
The Virtual Telescope Project in Rome is offering a free online viewing session of asteroid Apophis on March 5-6, 2021. The feed starts March 6 at 00:00 UTC (March 5 at 7:00 pm EST; translate UTC to your time).
Click here for more information about the Virtual Telescope live view of asteroid Apophis on March 5-6, 2021.
Previous observations with radar observations Goldstone and Arecibo confirmed that Apophis is elongated in shape. Image via NASA / JPL.
In addition, astronomers plan to study asteroid Apophis in April 2021 using NASA’s NEOWISE infrared space telescope. This is the same telescope that discovered 2020’s favorite comet, comet NEOWISE, which has now disappeared from view.
After the 2029 pass, asteroid Apophis will also make remarkable passes near Earth in 2036 and again in 2068. Earth attacks in 2029 and 2036 are excluded. As of February 2021, the chance of impact during the Apophis flyby in 2068 is now 1 in 380,000. That’s a 99.99974% chance that the asteroid will miss Earth in 2068.
The Apophis observations in 2021 should further improve our understanding of the asteroid’s shape and rotation, and they will help reduce the uncertainties in the space rock’s orbit caused by the so-called Yarkovsky acceleration.
In some cases, acceleration – a change in the speed and direction of an object through space – can help avoid a collision. Studies of the Yarkovsky acceleration associated with asteroid Apophis suggest this is the case for this asteroid. Previous calculations (made in 2016) had anything but ruled out the chance of an impact in 2068. The probability of an impact was considered vanishing in 2016, with only 1 in 150,000 impact probabilities, or a 99.99933% chance that the asteroid would miss Earth.
The more recent observations, first discussed in October 2020 and updated again in early 2021, show a decreasing risk.
It’s a Yarkovsky acceleration of asteroid Apophis – detected by University of Hawaii astronomers – that reduced the likelihood of a flight impact in 2068.
Orbit of asteroid Apophis (pink) as opposed to Earth’s orbit (blue). The yellow dot represents the sun. Apophis takes 323.6 days to orbit the sun. Earth lasts 365.3 days. Thus, this asteroid is a fairly frequent visitor to our region of space. Image via Phoenix7777 / Wikimedia Commons.
Astronomer Dave Tholen and his colleagues used the 323-inch (8.2-meter) Subaru telescope in Maunakea, Hawaii, to make the most recent observations. These astronomers were then able to update the risk of an earth collision from Apophis, including the latest measurements of the Yarkovsky effect, which stems from a miniscule push caused by sunlight.
Visit the Apophis page in the Center for Near Earth Object Studies
The new work from Tholen and colleagues suggests that Apophis – with an estimated diameter of between 1,115 and 1,214 feet (340 to 370 meters) – drifts more than 500 feet (about 170 meters) per year from its expected position in its orbit.
Tholen has been following the movement of Apophis in the sky since he and his colleagues discovered it on June 19, 2004, from Kitt Peak National Observatory near Tucson, Arizona. He noted in the statement:
We have known for some time that an impact with Earth is not possible during the close approach of 2029.
The new observations we have obtained with the Subaru telescope [in 2020] were good enough to reveal Apophis’ Yarkovsky acceleration, and they show the asteroid drifting about 170 meters from a purely gravitational orbit [about 500 feet] per year, which is sufficient to maintain the 2068 impact scenario.
These observations are not easy to obtain and analyze. Factors such as the distance of the asteroid at the time of observation, its composition, shape, and surface features all influence the outcome.
But astronomers are trying to understand the orbit of asteroid Apophis because of its brief movements around our planet in this century and beyond.
Read more about the Yarkovsky effect: pushing asteroids around with sunlight
Apophis isn’t the only asteroid near Earth, of course. In recent years, astronomers have been able to find and track many small asteroids sweeping near Earth. For example, on September 24, 2020, asteroid 2020 SW flew even closer to us than our meteorological and television satellites, as well as other geostationary satellites, orbiting our planet about 22,300 miles (35,900 km) from Earth’s surface. Asteroid 2020 SW came within about 7% of the Earth-Moon distance. But asteroid 2020 SW is estimated to be only about 14 to 32 feet (about 4.5 to 10 meters) in diameter. That is very small in contrast to asteroid Apophis.
This animation shows the distance between the asteroid Apophis and Earth at the time of the asteroid’s closest approach in 2029. The blue dots are man-made satellites orbiting our planet, and the pink represents the International Space Station. Image via NASA / JPL-Caltech.
The 2029 pass of asteroid ApophisApophis’ meeting with Earth on April 13, 2029 will be extraordinarily close. At its closest in 2029, Apophis will sweep just 23,441 miles (37,725 km) from our planet, or about 10% of the Earth-Moon distance. That’s very close for a space rock over 340 meters wide! Lance Benner from NASA / JPL commented:
This is the closest thing to anything as big as it is currently known. (In 2029) Apophis will be visible to the naked eye for several hours, and Earth’s tides are likely to change rotational states.
Friday April 13, 2029 will be showtime for asteroid Apophis, for both the general public and astronomers. Apophis will get so close that it will only be visible to the naked eye; something that almost never happens with asteroids. According to NASA, Apophis will become visible for the first time in the Southern Hemisphere and will look like a speck of light moving across Australia during this close-up encounter. It will be over the Atlantic Ocean at Earth’s closest approach. It will be so fast that it will cross the Atlantic Ocean in just an hour and cross the US in the late afternoon / early evening the next hour. Calculations indicate that Apophis will reach a visual magnitude of 3.1 during this approach, comparable to the stars in the Little Bear. By 2029, Apophis is expected to be visible to the naked eye from some parts of Australia, West Asia, Africa and Europe.
Like many asteroids, Apophis has been classified as a potentially dangerous asteroid by the International Astronomical Union’s Minor Planet Center. That simply means that it is an asteroid whose orbit occasionally brings it close to Earth, large enough to cause “significant regional damage” in the event of a collision. A survey by the NEOWISE spacecraft in 2012 suggested that there are 4,700 ± 1,500 potentially dangerous asteroids with a diameter of more than 100 meters.
According to some estimates, an asteroid the size of Apophis could strike Earth about every 80,000 years.
As a result of the extremely close approach in April 2029, perturbations caused by Earth’s gravity are expected to alter Apophis’ orbit from the Aten to the Apollo class. Image via NASA / JPL.
In short, the orbit of asteroid Apophis past Earth this week will be the closest for its extraordinarily short 2029 pass. This March 5-6, 2021 pass will be 44 times further away than the moon’s orbit. Apophis is a relatively large body, notable for its very close approach to Earth in 2029, 2036 and 2068. Astronomers’ observations indicate that it is extremely unlikely that Apophis will hit Earth this century.
Read more about the Yarkovsky effect: pushing asteroids around with sunlight
Via CNEOS
