U Scorpii erupts (and an update on V496 Scuti)

Nova in Latin means new. This is an apt name for a type of star that appears to brighten from out of nowhere. A small sub-class of these objects, called recurrent novae, have been observed to erupt on multiple occasions. U Scorpii is such an object having been observed in outburst in 1863, 1906, 1917, 1936, 1945, 1969, 1979, 1987, and 1999. Recent studies suggested another outburst was due in 2008-2010 and this study appears correct. On Jan 28, Barbara Harris of New Smyrna Beach, Florida imaged U Sco at a relatively bright magnitude of V = 8.05 (bright enough for binoculars and small telescopes). Only a night earlier Harris had measured its brightness at a dim V = 18.2.

U Scorpii is a “fast” nova meaning it rapidly decreases in brightness. The chart below shows the rapid decrease in brightness of roughly a magnitude per day. Though I didn’t attempt to observe the nova, Salvador Aguirre was able to observe it visually on 4 consecutive nights (the blue crosses on the chart below). The nova is now around magnitude 14 which is too faint for all but CCD-equipped astronomers.

Much more on the history and science of U Sco can be found at the AAVSO.

While U Sco is am example of a fast nova, another nova first seen in November is of the “slow” variety. V496 Scuti was an easy object for evening observers and I was able to observe it over the course of a few weeks. Unfortunately the object got too low to be seen from my backyard and I had to stop my observations. After a month or so too close to the Sun for any observers, the nova is once again visible. Surprisingly the nova is still a reasonably bright 9th magnitude and only ~1.5 to 2.0 magnitude fainter than at maximum. That’s a fading of 1.5 to 2.0 magnitude over a 2+ month period. Compare that with U Sco’s rate of ~1 magnitude per day. More on this object can be found on earlier Transient Sky posts here and here.

Hubble Images “Comet” P/2010 A2 (LINEAR)

Last month an apparent “comet” was discovered in the inner part of the usually asteroidal Main Belt. Early observations quickly uncovered an object that looked less like a comet and more like the result of a traumatic event on an asteroid. Whether that event was due to a collision between 2 small asteroids or the break-up of an asteroid due to rapid rotation has not yet been determined, but these 2 explanations seem to be the most likely. It would be the 1st time we’ve observed either of these processes in real-time. For more on this object, which is still named Comet P/2010 A2 (LINEAR), see the post titled “The Curious Case of Comet LINEAR“.

David Jewitt (UCLA) led a team which used the Hubble Space Telescope (HST) to take the highest resolution images of the “comet” yet. [See the HST press release here.] Ground-based images have not recorded much detail in the dust trail. The superior resolution of HST (it really helps to observe above the Earth’s atmosphere) fines a number of criss-crossing linear features. The remains of the asteroid that released the dust can be seen as the faint star leading (to the lower left) the dust trail. Hopefully data from HST as well as an assortment of other telescopes will allow modelers to determine what caused the event. I’m sure this will not be the last update on this unique object.

HST image of P/2010 A2. Credit: NASA, ESA, David Jewitt (UCLA).

In The Sky This Month – February 2010

This feature highlights a number of meteor showers, comets and asteroids which are visible during the month of February 2010. Mars is at its closest and brightest at the beginning of the month. Though it will quickly fade it will remain the dominant planetary body in the evening sky this month.

Note: If anyone has pictures or observations of these objects/events and want to share them, send me a comment and I’ll post them on the blog.

Planets

Venus - Venus is starting its slow climb higher in the evening sky. For the entire month, Venus will only be visible for ~20 minutes after sunset at the start of the month and ~50 minutes after sunset at the end of February. As a result, you will need a clear view of the southwest horizon to see it. Venus will be much higher and easier to see over the next few months. For northern observers, it will be highest in June. The best time for southern observers will be August.

Feb 14 - Moon passes 5° from Venus
Feb 17 - Venus and Jupiter within 0.5° of each other

Jupiter - This month is the last month to see Jupiter in the evening sky. At magnitude -2.0, the King of the Planets is very low in the southwest sky after dusk. By the end of the month it is pretty much invisible to all observers. Observers with a clear SW horizon can watch Jupiter, Venus and the Moon put on a nice show during the middle of the month.

Feb 15 - Moon passes 5° from Jupiter
Feb 17 - Jupiter and Venus within 0.5° of each other

Mars – Mars was at opposition (the point opposite the Sun in the sky) on January 29. Opposition means Mars is closest to Earth and at its brightest. It also means it is visible nearly all night long, rising in east in the early evening, at its highest around midnight, and setting in the west around dawn.

This month the Earth and Mars are slowly moving away from each other. As a result, Mars will quickly fade from magnitude -1.3 to -0.6. Still it will be a brilliant red beacon in the ENE sky right after sundown outshining all but the brightest stars. Note that unlike the stars which twinkle, Mars shines with an unwavering red glow.

Feb 26 - Moon passes close (5°) to Mars

Saturn – Saturn is easy to observe during the morning hours and is sufficiently high enough to be observed in the eastern sky by midnight. Located in Virgo, the planets will appear as bright as a magnitude +0.7 star. Telescope users should note that Saturn’s rings are still close to edge-on.

Feb 2 - Moon and Saturn within 8° of each other

Mercury – Mercury is in the morning sky this month. Northern observers will be able to spot it early in the month as it quickly falls back into the twilight glow. In the south, Mercury starts the month nearly as high as it can get and it should remain visible (with increasing difficulty) for the remainder of the month.

Feb 12 - Moon passes 2° from Mercury

Meteors

February hosts one of the better annual showers of the year in the Quadrantids. Unfortunately this year’s display will be wrecked by bright moonlight. The background rate of meteors crashes in January.  The year is usually split in 2 with January through June having low rates with few major showers while July through December (really through the 1st week of January) have high rates with many major showers.

Sporadic Meteors

Sporadic meteors are not part of any known meteor shower. They represent the background flux of meteors. Except for the few days per year when a major shower is active, most meteors that are observed are Sporadics. This is especially true for meteors observed during the evening. During January, 8-10 or so Sporadic meteors can be observed per hour from a dark moonless sky.

Major Meteor Showers

No major showers this month.

Minor Meteor Showers

Minor showers produce so few meteors that they are hard to notice above the background of regular meteors. Starting this month, info on most of the minor showers will be provided on a weekly basis by Robert Lunsford’s Meteor Activity Outlook.

Additional information on these showers and other minor showers not included here can be found at the following sites: Wayne Hally’s and Mark Davis’s NAMN Notes, and the International Meteor Organization’s 2008 Meteor Shower Calendar.

Comets

Naked Eye Comets (V < 6.0)

None

Binocular Comets (V = 6.0 – 8.0)

None

Small Telescope Comets (V = 8.0 – 10.0)

Comet 81P/Wild 2

Comet Wild 2 is a short-period Jupiter-family comet on a 6.4 year orbit. In 1974 a close approach to Jupiter placed the comet on its current orbit which allows (relatively) close approaches to the Sun and Earth. Swiss professional astronomer Paul Wild found the comet photographically on its first close perihelion in 1978. During its last perihelion passage it was the target of the NASA Stardust spacecraft which flew through its coma, collected cometary dust, and returned the dust to Earth. Though Wild 2 has become bright enough to be seen in small backyard telescopes before, this year’s apparition will be its best since discovery. Not till 2042 will it come closer, and even then only marginally so.

This year Wild 2 will reach perihelion on February 22 at 1.60 AU and closest approach to Earth will occur on April 5 at 0.67 AU. Though the comet will only reach a brightness of magnitude ~9.2 to 9.5 in March, it will remain brighter than magnitude 10.0 from January through May.

Currently the comet is around magnitude 9.5 to 10.0 and should be around magnitude 10.0 or even brighter by the end of the month. At mid-month the comet is located in Virgo (not far from Saturn) at a distance of 1.60 AU from the Sun and 1.86 AU from Earth.

A finder chart for Comet Siding Spring can be found at Comet Chasing and Aktuelle Kometen (in German).

A nice collection of images can be found at the VdS-Fachgruppe Kometen (Comet Section of Germany) and Seiichi Yoshida’s Comet Homepage.

Comet C/2007 Q3 (Siding Spring)

This long-period comet was first seen on 2007 August 25 by Donna Barton of the Siding Spring Survey in Australia. This past Oct. 7th the comet reached a rather distant perihelion at 2.25 AU from the Sun. Unfortunately, the comet and Earth are located on opposite sides of the Sun so the comet is rather far from Earth. Still the comet is observable in the early morning hours as a slowly fading ~9.5 to 10.5 magnitude comet in Bootes. At mid-month the comet is 2.69 AU from the Sun and 2.21 AU from Earth.

A finder chart for Comet Siding Spring can be found at Comet Chasing and Aktuelle Kometen (in German).

A nice collection of images can be found at the VdS-Fachgruppe Kometen (Comet Section of Germany) and Seiichi Yoshida’s Comet Homepage.

Asteroids

Binocular and Small Telescope Asteroids (V < 9.0)

(4) Vesta

Though not as large as Ceres, Vesta is more reflective making it the brightest asteroid in the Main Belt. Vesta is peculiar in that it appears to have evidence of volcanism on its surface. Similar to the Moon, Vesta may be covered with large expanses of frozen lava flows. It is classified as a V-type asteroid and is the only large asteroid with this classification. Many of the smaller V-type asteroids are chips of Vesta blasted off it by past asteroid and comet impacts. Vesta is similar in size to Pallas with dimensions of 347×336x275 miles or 578×560×458 km. Vesta will also be visited by NASA’s Dawn spacecraft which will arrive in 2010.

Vesta starts the month at magnitude 6.4 and brightens to a maximum of 6.1 at opposition on Feb 18. By the end of the month, it has already started to fade at magnitude 6.2. Sixth magnitude is close to the brightest Vesta can get and is easy for binocular observers. If you are lucky enough to be located in a very dark rural site you may even be able to see Vesta by naked eye among the stars of Leo.

A finder chart (needs to be flipped upside down for Northern Hemisphere observers) can be found at the Royal Astronomical Society of New Zealand. Finder chart for Vesta from Heavens Above.

Meteor Activity Outlook for January 30-February 5, 2010

The Meteor Activity Outlook is a weekly summary of expected meteor activity written by Robert Lunsford, Operations Manager of the American Meteor Society and contributor to this blog. The original unedited version of this week’s Meteor Activity Outlook can be found at the American Meteor Society’s site.

February offers the meteor observer in the northern hemisphere a couple of weak showers plus falling sporadic rates. This may not seem too exiting but you never know when surprises are in store. An errant earthgrazer from the Centaurid complex may shoot northward. Better yet, a bright fireball may light up the sky. February is the start of the fireball season, when an abundance of fireballs seem to occur. This lasts well into April and seems to occur mostly during the early evening hours.

Observers in the southern hemisphere are treated to the Alpha Centaurid peak on the 8th plus the entire Centaurid complex of radiants is active all month long. Sporadic rates are slightly less than those seen in January, but still stronger than those witnessed north of the equator.

During this period the moon reaches its first quarter phase on Saturday January 30th. At this time the moon will be in the sky all night long making meteor observing difficult at best. As the week progresses the moon will rise later and later in the evening offering a few hours of dark sky between the end of evening twilight and moonrise. The estimated total hourly rates for evening observers this week is ~1 for those in the northern hemisphere and ~2 for those south of the equator. For morning observers the estimated total hourly rates should be ~8 from the northern hemisphere and ~10 as seen from the southern hemisphere. The actual rates will also depend on factors such as personal light and motion perception, local weather conditions, alertness and experience in watching meteor activity. Meteor rates this week are reduced by strong moonlight.

The radiant positions and rates listed below are exact for Saturday night/Sunday morning January 30/31. These positions do not change greatly day to day so the listed coordinates may be used during this entire period.

The full descriptions of each active meteor shower will continue next week when the moon becomes less of a nuisance to observers.

The list below presents a condensed version of the expected activity this week. Rates and positions are exact for Saturday night/Sunday morning.

Shower Name                RA     DEC   Vel     Rates
                                        km/s   NH    SH
ANT Antihelions          09h 36m  +13    30     2     1
DLE Dec Leonis Minorids  13h 12m  +12    64    <1    <1
ACE Alpha Centaurids     13h 20m  -57    56    <1     1

RA - Right Ascension
DEC - Declination
Vel - Velocity relative to Earth (in km per sec)
Rates - Rate of visible meteors per hour from a
        dark site
NH - Northern Hemisphere
SH - Southern Hemisphere

Jan 24/25/26/27/28 Meteors

Not much to report from the past few nights. Last night was rained out and the previous 2 were hampered by lots of passing cirrus. The long-range forecast calls for a wet February which is great for breaking our drought but not for meteor watching.

The big meteor-related news was the video detection of a minor outburst by the very poorly observed shower, the Gamma Ursae Minorids (reported on CBET 2146). A network of 6 video meteor cameras in Finland detected 10 meteors from this shower on the night of Jan 20/21. Unfortunately my cameras, as well as Bob’s, were offline that night due to bad weather. Even if it were clear we might not have recognized anything. The 6 Finnish cameras only saw 4, 1, 1, 1, 3 and 2 meteors apiece (this adds up to more than 12 because some meteors were seen by multiple cameras). It was only after combining data from the 6 cameras that the shower was obvious.

Until last week the shower was only known from Canadian radar observations. Since radar detects meteors that are much smaller, and hence fainter, than those seen visually or by video, the thinking was that this shower is too faint for us video and visual observers. But a quick search of Sirko Molau’s IMO Video Meteor Database (of which my and Bob’s cameras are members) shows this to not be the case. The Gamma Ursae Minorid radiant shows up as one of the most productive radiants for a 3 night period ending on Jan 20/21. These radiants were determined from 100,000s of meteors observed over the past decade or more.

Even though it is easy to go back and find evidence of this shower now, it is one of many possible minor showers that are hard to verify as real with much confidence. As more and more observations are made, don’t be surprised if the number of recognized showers increases by the hundreds.

Obs  Date(UT)      Time    TOT SPO ANT DLM
TUS  2010-01-28   00h 00m Clouds - No Meteors
TUS  2010-01-27   10h 09m   2   2   0   0
TUS  2010-01-26   11h 49m   2   1   0   1
TUS  2010-01-25   11h 49m   14  12  1   1      

TUS - Camera in Tucson operated by Carl Hergenrother
SDG - Camera in San Diego operated by Bob Lunsford
TotTime - Total amount of time each camera looked for meteors
TOT - Total number of meteors detected
SPO - Sporadics (meteors not affiliated with any particular meteor shower)
ANT - Antihelions
DLM - December Leonis Minorids

Jan 23/24 Meteors

After almost a week of clouds and rain, it was once again clear enough for meteor watching last night. The much publicized series of strong winter storms did not disappoint with many reports of tornadoes, hurricane force winds, and heavy rain across much of the American Southwest. The 4th of the 5 storms, which passed through Arizona Thursday night, broke records across much of Arizona for lowest recorded barometric pressure.

Here in Tucson, the story was the much needed rain. Approximately 2.3″ of rain fell at my house. A few more good rain-soakers this winter would go a long way towards alleviating our decade long drought. Go El Nino…

For the past month I’ve had 3 cameras set up (my 2 small FOV cameras and an all-sky fireball camera). The all-sky camera was located on the roof of my house and was only held in place by a few bricks. Since winds were forecast to be so high last week, I decided to take the camera down. While on the roof I took a peak at my other 2 cameras and found that the glass window of one of the all-weather housing was loose. In fact, it was almost completely debonded from the metal housing and resting on the camera’s lens. If I hadn’t noticed this, I’d probably be dealing with one thoroughly soaked (and probably dead) camera and lens. So for the next few nights only the zenith pointing meteor camera will be operating.

Sporadic activity remains healthy. Then again with only 2 very minor showers active, most meteors are sporadics. We are nearing the end of activity for the December Leonis Minorids which have been producing about 10-20% of all meteor activity since mid-December (with the exception of a few nights around the Geminid and Quadrantid maximums).

Obs  Date(UT)      Time    TOT SPO ANT DLM JLE
TUS  2010-01-24   05h 30m   14  13  1   0   0   

TUS - Camera in Tucson operated by Carl Hergenrother
SDG - Camera in San Diego operated by Bob Lunsford
TotTime - Total amount of time each camera looked for meteors
TOT - Total number of meteors detected
SPO - Sporadics (meteors not affiliated with any particular meteor shower)
ANT - Antihelions
DLM - December Leonis Minorids
JLE - January Leonids

Meteor Activity Outlook for January 23-29, 2010

The Meteor Activity Outlook is a weekly summary of expected meteor activity written by Robert Lunsford, Operations Manager of the American Meteor Society and contributor to this blog. The original unedited version of this week’s Meteor Activity Outlook can be found at the American Meteor Society’s site.

January sees a peak of sporadic activity for the southern hemisphere while rates seen north of the equator begin a steady downward turn that continues throughout the first half of the year. The sporadic activity is good for both hemispheres, but not as good as it was for northern observers in December. Once the Quadrantids have passed the shower activity for January is very quiet.

During this period the moon reaches its first quarter phase on Saturday January 23rd. At this time the moon will be limited to the evening hours and will set near midnight local standard time (LST). As the week progresses the moon begins to interfere into the active morning hours as it sets later and later with each passing night. Toward the end of the period the nearly full moon will be in the sky nearly all night long. This will make observations difficult at best. The estimated total hourly rates for evening observers this week is ~3 no matter your location. For morning observers the estimated total hourly rates should be ~15 from the northern hemisphere and ~16 as seen from the southern hemisphere. The actual rates will also depend on factors such as personal light and motion perception, local weather conditions, alertness and experience in watching meteor activity. Rates are reduced this week due to moonlight.

The radiant positions and rates listed below are exact for Saturday night/Sunday morning January 23/24. These positions do not change greatly day to day so the listed coordinates may be used during this entire period.

The following showers are expected to be active this week.

Antihelion (ANT)

The wide Antihelion (ANT) radiant is now centered at 09:08 (137) +15. This area of the sky lies in eastern Cancer. The bright orange planet Mars, now near opposition, lies to northwest of this position. This radiant is best placed near 0100 LST when it lies on the meridian and is located highest in the sky. Due to the large size of this
radiant, any meteor radiating from northwest Hydra, western Leo, or Cancer could be a candidate for this shower. Rates at this time should be ~2 per hour as seen from the northern hemisphere and ~1 per hour for observers located south of the equator. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of medium-slow speed.

December Leonis Minorids (DLM)

The December Leonis Minorids (DLM) are near the end of their activity period. A few stragglers from this radiant may still be seen from a radiant located at 12:46 (192) +15. This position lies in southern Coma Berenices. The nearest star of note would be third magnitude Epsilon Virginis, located five degrees to the southeast. These meteors are best seen near 0500 LST when the radiant lies highest above the horizon. This shower peaked on December 20th so current rates would be near < 1 per hour no matter your location. At 64km/sec. the December Leonis Minorids produce mostly swift meteors.

The table below presents a condensed version of the expected activity this week. Rates and positions are exact for Saturday night/Sunday morning but may be used all week long.

Shower Name                RA     DEC   Vel     Rates
                                        km/s   NH    SH
ANT Antihelions          09h 08m  +15    30     2     1
DLE Dec Leonis Minorids  12h 46m  +15    64    <1    <1

RA - Right Ascension
DEC - Declination
Vel - Velocity relative to Earth (in km per sec)
Rates - Rate of visible meteors per hour from a
        dark site
NH - Northern Hemisphere
SH - Southern Hemisphere

Jan 9/10 to 17/18 Meteors

We are in the midst of the early year doldrums, meteor-wise. Rates are low and will remain so until the Lyrids flare up in April. Still a surprise outburst can happen at any time so my 2 cameras will be running every clear (and even most cloudy) nights.

The large scatter in nightly meteor detections is due to changes in sky conditions. For example, it was cloudy most of the night. Luckily I was able to grab a single meteor in a short-lived hole in the clouds (what astronomers affectionately call a “sucker hole”). The weather forecast is pretty bad for the rest of the week. Though to be honest, I’ll be glad to trade a week’s worth of meteors for a few inches of much-needed rain.

Bob’s notes from the night of Jan 14/15 : “Skies were clear again tonight but the good meteor rates seen during the first half of the month are now half their prior strength. The drop in rates is usually a bit more gradual this time of year.”

… from the night of Jan 12/13 : “On the 13th, I only observed three meteors before the skies were clouded over the remainder of the night. Skies were much better tonight but the meteor activity was low.”

… from the night of Jan 11/12 : “This was another dusk to dawn session. Despite the occasional interference from cirrus clouds, rates were good for this time of year.”

… from the night of Jan 10/11 :  “The night of the 10th was lost due to thick cirrus. The skies had cleared during the day allowing dusk to dawn coverage on the 11th. Normal rates for this time of the year were observed.”

Obs  Date(UT)      Time    TOT SPO ANT DLM JLE XCB SCC
TUS  2010-01-18   00h 30m   1   1   0   0   0   -   0
TUS  2010-01-17   11h 46m   15  11  1   3   0   -   0
TUS  2010-01-16   07h 39m   3   2   0   1   0   0   0
TUS  2010-01-15   11h 54m   15  12  1   1   0   0   0
SDG  2010-01-15   09h 12m   33  27  2   4   -   0   0
TUS  2010-01-14   11h 14m   6   3   0   3   0   1   -
SDG  2010-01-14   10h 53m   29  22  4   3   -   0   -
TUS  2010-01-13   12h 02m   14  12  2   0   0   0   -
SDG  2010-01-13             3   3   0   0   -   0   -
TUS  2010-01-12   11h 44m   22  17  4   1   0   0   -
SDG  2010-01-12   11h 37m   54  44  4   4   -   2   -
TUS  2010-01-11   06h 28m   22  14  1   4   0   3   -
SDG  2010-01-11   11h 40m   49  40  5   4   -   -   -
TUS  2010-01-10   11h 49m   8   6   2   0   0   0   -
SDG  2010-01-10   00h 00m   Clouds / No Meteors

TUS - Camera in Tucson operated by Carl Hergenrother
SDG - Camera in San Diego operated by Bob Lunsford
TotTime - Total amount of time each camera looked for meteors
TOT - Total number of meteors detected
SPO - Sporadics (meteors not affiliated with any particular meteor shower)
ANT - Antihelions
DLM - December Leonis Minorids
AHY - Alpha Hydrids
JLE - January Leonids
QUA - Quadrantids
XCB - Xi Coronae Borealids

A Few Notes about 2010 AL30

“Mysterious Object Hurtles Towards Earth”

“Weird Object Zooming by Earth Wednesday is Likely an Asteroid”

“Mysterious Space Object Rocks the Web”

The small asteroid 2010 AL30 has made quite a splash in the news today. The titles above are just some examples of news stories floating around the internet. Unfortunately the large number of news stories and blogs calling this object a “mystery” sheds a lot of light on how bad modern reporting can be. As the 3rd headline story above put it: “Something is hurtling toward the planet. And we say ’something’ because neither we, nor anybody in the scientific field, seems to know exactly what it is.”

Well not quite…

We know exactly what it is. It’s a small asteroid. Sure we don’t know what kind of asteroid it is (is it stoney, basaltic, carbonaceous, iron-nickel?) but those observations will be made soon if they haven’t already. We know the asteroid’s orbit, where it’s been and will be in the future.

The “mystery” part seems to be based on early speculation that AL30 was a returning piece of long-lost space hardware. Such speculation is not crazy and there have been examples of this in the past. An object discovered in 2002 turned out to be the Saturn IVB upper stage from Apollo 12 (I had a small part in confirming its man-made origin). Every time a small asteroid is found on a Earth-like orbit, there is always speculation that it is man-made. Such speculation is usually quickly refuted.

Much of the early speculation of AL30 was posted on the Minor Planet Mailing List (MPML), a Yahoo Groups forum used by amateurs and professionals interested in the observations of asteroids. It is a great forum for sharing ideas and calling attention to interesting observations though the level of expertise ranges from expert to novice. The possibility of AL30 being artificial was quickly brought up on the MPML and then just as quickly refuted. Unfortunately that short exchange was enough to get the asteroid labeled as “mysterious”. Once one trusted news source calls it a “mystery” it isn’t long before the average “copy and paste” stories spread like wild fire.

Even if AL30 was man-made, it really wouldn’t be much of a mystery. We’d quickly figure out what launch it was a part of. It’s orbit is now well determined allowing the NEO Project Office at JPL to find no instances of a previous close approach to Earth in the past 50 years. This rules out a man-made origin. Then again calling it a “mystery” in the press may get more people to read the story. Science can be boring if we have all the answers. Maybe by making it seem that we are uncertain of something, it makes it appear that we can’t rule out anything (maybe its an asteroid, a comet, a man-made spacecraft, maybe even something secret, or an UFO) and that makes for a better story.

Enough ranting, what do we actually know about 2010 AL30…

Not much has changed from my previous posting on the object. It is still predicted to pass within 129,000 km of Earth tomorrow morning (Jan 13) at ~12:46 UT.  The figure below by JPL shows its path through cislunar space.

Path of 2010 AL30 on Jan 13. Credit: NASA/JPL.

What if AL30 were to hit the Earth? How much of an impact (no pun intended) would it make?

A group at the University of Arizona/Lunar and Planetary Lab has created a web GUI (called the Earth Impact Effects Program) that estimates the effect of an impacting asteroid on Earth. Entering in the following parameters for AL30 (these are just estimates but are realistic based on our current knowledge of the object):

Inputs:

• Projectile Diameter: 15.00 m = 49.20 ft = 0.01 miles
• Projectile Density: 3000 kg/m³
• Impact Velocity: 9.50 km/s = 5.90 miles/s
• Impact Angle: 45 degrees
• Target Density: 2500 kg/m³

gives us the following results …

Energy:

• Energy before atmospheric entry: 2.39 x 10¹⁴ Joules = 0.57 x 10^-1 MegaTons TNT
• The average interval between impacts of this size somewhere on Earth is 12.1 years

Atmospheric Entry:

• The projectile begins to breakup at an altitude of 44700 meters = 147000 ft
• The projectile bursts into a cloud of fragments at an altitude of 22900 meters = 75100 ft
• The residual velocity of the projectile fragments after the burst is 6.12 km/s = 3.8 miles/s
• The energy of the airburst is 1.40 x 10¹⁴ Joules = 0.33 x 10^-1 MegaTons.
• No crater is formed, although large fragments may strike the surface.

This would be one nice fireball and look very similar to many of the bright ones reported on this blog. Small pieces of the asteroid would probably survive to reach the ground as meteorites. Note, this group states that a 15-meter asteroid should hit the Earth once every 12 years while in yesterday’s posting I said once every 50 years. The once every 50 years number comes from global infrasound data and the every 12 year interval from asteroid survey data. It is probably safe to say that a 15-meter impact happens once every 10-50 years.

One other caveat, the above calculation assumes the asteroid is a fractured rock. If it were a solid piece of nickel-iron, the impact would be much greater as seen below.

Atmospheric Entry:

• The projectile begins to breakup at an altitude of 3470 meters = 11400 ft
• The projectile reaches the ground in a broken condition. The mass of projectile strikes the surface at velocity 5.65 km/s = 3.51 miles/s
• The impact energy is 2.26 x 10¹⁴ Joules = 0.54 x 10^-1MegaTons.
• The broken projectile fragments strike the ground in an ellipse of dimension 0.101 km by 0.0714 km

Crater Dimensions:

• Crater shape is normal in spite of atmospheric crushing; fragments are not significantly dispersed.
• Final Crater Diameter: 427 m = 1400 ft
• Final Crater Depth: 91 m = 299 ft
• Richter Scale Magnitude: 3.7

Luckily nickel-iron meteorite falls are very rare and a very minor fraction of all impactors.

Remember to Duck Wednesday Morning

A very small, newly discovered asteroid will make a close flyby of Earth this Wednesday. 2010 AL30 was first seen by the LINEAR survey (same group that discovered the unusual comet P/2010 A2) on Jan 10 UT. The asteroid will pass ~80,000 miles or 128,000 km (0.00086 AU) from Earth at ~12:45 UT on Jan 13 (Wednesday morning).

With an absolute magnitude of 27.0, the asteroid is probably on the order of 10 to 20 meters in diameter. Though it will safely miss the Earth, even if it were to hit it would be unlikely to do any damage as very little of it would survive passage through the atmosphere. A recent paper by Peter Brown (University of Western Ontario) determined the rate of impact for small asteroids based on global infrasound observations. An object 15 meters in diameter should hit the Earth once every ~50 years. Based on that statistic the detection of an object like 2010 AL30 should be rare. But the Earth is a small target. Extrapolating the Earth collisional volume to the volume of space within the distance of the Moon finds that ~600 objects of the size of 2010 AL30 pass within a lunar distance every year. These kinds of close approaches are not rare, and the great majority of them are missed by the current asteroid surveys which are optimized to find much larger (and actually dangerous) objects.

The orbit of 2010 AL30 is a typical near-Earth asteroid orbit (see the diagram below). It stretches from 0.70 to 1.30 AU from the Sun. With a semi-major axis of 1.001 AU, its orbital period is almost exactly the same as Earth’s. At its brightest the asteroid will reach magnitude ~14 which is far too faint to be seen by all but the most well equipped amateurs.

Orbits and positions of 2010 AL30 and the inner planets for 2010 Jan 13. Created with C2A.

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