Astronomy Essentials

Comet Halley, parent of 2 meteor showers

Comet Halley: A rocky body hurtling through space, surrounded by a cloud of haze.
View larger. | The Halley Multicolor Camera on ESA’s Giotto spacecraft captured this image of the nucleus of Comet Halley. This image was the Astronomy Picture of the day for January 4, 2010.

Comet Halley visited last in 1986

The famous comet 1P/Halley – aka Halley’s Comet – swings into the inner solar system about every 76 years. At such times, the sun’s heat causes the comet to loose its icy grip over its mountain-sized conglomeration of ice, dust, and gas. And so, at each pass, the crumbly comet sheds a fresh trail of debris into its orbital stream. It lost about 1/1,000th of its mass during its last flyby, in 1986. And it so happens we intersect Halley’s Comet’s orbit not once, but twice each year. That’s why – although the comet itself is nowhere near – Halley’s Comet is the parent of not just one, but two well-known annual meteor showers, one in May and one in October.

In early May, we see bits of this comet as the annual Eta Aquariid meteor shower.

Then some six months later, in October, Earth in its orbit again intersects the orbital path of Halley’s Comet. This time around, these broken-up chunks from the comet burn up in Earth’s atmosphere as the annual Orionid meteor shower.

And, by the way, Halley is pronounced like valley. According to Ian Ridpath:

Many people nowadays say “Hailey”, a legacy of the 1950s rock group Bill Haley and the Comets.

Long streak with bright rounded end on star field.
Compare this image to the one at top. Here’s how we saw Comet Halley on May 29, 1910. Image via Wikimedia Commons.

Comet debris litters the comet’s orbit

Because Halley’s Comet has circled the sun innumerable times over countless millennia, cometary fragments litter its orbit. That’s why the comet doesn’t need to be anywhere near the Earth or the sun in order to produce a meteor shower. Instead, whenever our Earth in its orbit intersects Halley’s Comet’s orbit, cometary bits and pieces – often no larger than grains of sand or granules of gravel – smash into Earth’s upper atmosphere, to vaporize as fiery streaks across our sky: meteors.

The diagrams below can help you visualize Earth’s orbit with respect to the path of Halley’s Comet.

Graphic showing path of Halley's Comet with respect to Earth's orbit.
The path of Halley’s Comet intersects the earth’s orbit twice each year. In early May it produces the Eta Aquariid meteor shower (left) as the particles leave the inner solar system. Diagram via JPL Horizons Program.
Graphic showing path of Halley's Comet with respect to Earth's orbit.
In mid-October, Halley’s Comet produces the Orionid meteor shower (right) as the particles enter the inner solar system. Diagram via JPL Horizons Program.
Lines marking constellation with radial arrows near middle of it.
The radiant point of the Eta Aquariid meteor shower is near the star Eta Aquarii in the constellation Aquarius the Water Bearer. The radiant rises in the wee hours after midnight and is still climbing toward its highest point – in the south as seen from the Northern Hemisphere – at dawn. It’s because we’re in a different part of our orbit – and have a unique perspective of the comet’s orbit – that the two meteor showers appear in different parts of the sky. See the illustration below.
Illustration of Orionid radiant point.
The Orionids are seen high in the northern morning sky, against a darker sky background.

Where is Halley’s Comet now?

Often, astronomers like to give distances of solar system objects in terms of astronomical units (AU), which is the sun-Earth distance. Halley’s Comet lodges 0.587 AU from the sun at its closest point to the sun (perihelion) and 35.3 AU at its farthest point (aphelion).

In other words, at its farthest, Halley’s Comet resides about 60 times farther from the sun than it does at its closest.

It was last at perihelion in 1986, and will again return to perihelion in 2061.

At present, this comet lies outside the orbit of the outermost major planet, Neptune, and not far from its aphelion point. It will reach aphelion in November-December, 2023.

So the comet is far away. Even so, meteoroids – bits of debris left behind in the comet’s orbit – swim throughout Halley’s Comet’s orbital stream. So each time Earth crosses the orbit of the comet, in May and October, these meteoroids turn into incandescent meteors once they plunge into the Earth’s upper atmosphere.

Complete orbit of Halley's Comet, elongated oval reaching from near the sun to beyond Neptune.
A diagram of Halley’s Comet seen from above the solar system plane. Via Ian Ridpath. Used with permission.
Oblique view of solar system showing Halley's Comet orbit at angle to orbits of planets.
The orbit of Halley’s Comet. The comet does not stay in the same plane as the planets but is tilted 18 degrees and it revolves around the sun in the opposite direction as the planets. Diagram produced by JPL Horizons Program.

Meteor showers and comets

Of course, Halley’s Comet isn’t the only comet that produces a major meteor shower …

Three of the comets in the table below are each responsible for two meteor showers. We’ve already discussed Halley’s Comet. The asteroid 2004 TG10, responsible for the Northern Taurids, is part of the Taurid Complex, which includes Comet Encke, itself producing the Southern Taurids. And, asteroid 2003 EH1, responsible for the Quadrantids appears to be part of the Machholz Complex, which also includes Comet 96P/Machholz, itself producing the Delta Aquariids.

Meteor Shower Parent Comet Peak Date Orbital Period Perihelion Aphelion
Quadrantids 2003 EH1 (asteroid Jan 4 5.52 yrs 1.19 AU 5.06 AU
Lyrids Comet Thatcher (1861 G1) Apr 23 413 yrs 0.92 AU 110 AU
Eta Aquariids Comet 1P/Halley May 6 75.3 yrs 0.59 AU 35.3 AU
Delta Aquariids Comet 96P/Machholz July 30 5.28 yrs 0.12 AU 5.94 AU
Perseids Comete 109P/Swift-Tuttle Aug 13 133 yrs 0.96 AU 51.2 AU
Draconids Comet 21P/Giacobini-Zinner Oct 8 6.62 yrs 1.04 AU 6.01 AU
Orionids Comet 1P/Halley Oct 21 75.3 yrs 0.59 AU 35.3 AU
S Taurids Comet 2P/Encke Nov 6 3.30 yrs 0.33 AU 4.11 AU
N Taurids 2004 TG10 (asteroid) Nov 13 3.34 AU 0.31 AU 4.16 AU
Leonids Comet 55P/Tempel-Tuttle Nov 17 33.2 yrs 0.98 AU 19.69 AU
Geminids 3200 Phaethon (asteroid) Dec 14 1.43 yrs 0.14 AU 2.40 AU
Ursids Comet 8P/Tuttle Dec 22 13.6 yrs 1.03 AU 10.38 AU


What are those asteroids doing here?

Until recently a comet was a comet, and an asteroid was an asteroid. But the more we have learned about abut them the more the lines between them became blurred. The long-held belief that meteor showers can come only from active comets has been challenged by the discovery of asteroids being the parent objects of meteor showers. Most notably are the asteroids 2003 EH1 generating the Quadrantids and 3200 Phaethon behind the Geminids.

One of three things is going on here, or a combination of them. Perhaps the asteroid was once a comet and at that time expelled material that causes the meteor shower. The comet then became exhausted and all we have left is a small rocky nucleus.

Another possibility is that the asteroid was once part of a comet that at one time expelled material to cause the meteor shower, then the asteroid broke off and the comet was perturbed into a different orbit.

Or maybe the asteroid is still emitting material. A recent example of this is the asteroid Bennu, seen here ejecting material from its surface.

Dark space rock against black space, with particles coming off it.
Asteroid Bennu, as imaged by the OSIRIS-REx spacecraft. Bennu ejected 11 plumes of dust into space from January 6 to February 18 as captured in this composite image. Image via NASA/ Goddard/ University of Arizona/ Lockheed Martin.

Bottom line: The famous Halley’s Comet spawns the Eta Aquariids in early May and the Orionids in October. The comet is presently as far from us as it gets. Other comets, and even some asteroids, produce meteor showers.

Read more about Halley’s Comet and find more about the pronunciation of the name

Posted 
May 18, 2022
 in 
Astronomy Essentials

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