Near-Earth supernova
Encyclopedia
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
that occurs close enough to the Earth (roughly less than 100 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s away) to have noticeable effects on its biosphere
Biosphere
The biosphere is the global sum of all ecosystems. It can also be called the zone of life on Earth, a closed and self-regulating system...
.
Effects on the planet
On average, a supernovaSupernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
explosion occurs within 10 parsec
Parsec
The parsec is a unit of length used in astronomy. It is about 3.26 light-years, or just under 31 trillion kilometres ....
s of the Earth every 240 million years. Gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
s are responsible for most of the adverse effects a supernova can have on a living terrestrial planet
Terrestrial planet
A terrestrial planet, telluric planet or rocky planet is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets are the inner planets closest to the Sun...
. In Earth's case, gamma rays induce a chemical reaction
Chemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...
in the upper atmosphere
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
, converting molecular nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
into nitrogen oxide
Nitrogen oxide
Nitrogen oxide can refer to a binary compound of oxygen and nitrogen, or a mixture of such compounds:* Nitric oxide, also known as nitrogen monoxide, , nitrogen oxide* Nitrogen dioxide , nitrogen oxide...
s, depleting the ozone layer
Ozone layer
The ozone layer is a layer in Earth's atmosphere which contains relatively high concentrations of ozone . This layer absorbs 97–99% of the Sun's high frequency ultraviolet light, which is potentially damaging to the life forms on Earth...
enough to expose the surface to harmful solar and cosmic radiation. Phytoplankton
Phytoplankton
Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
and reef
Coral reef
Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...
communities would be particularly affected, which could badly deplete the base of the marine food chain.
Risk by type
Speculation as to the effects of a nearby supernova on Earth often focuses on large stars as Type II supernova candidates. Several prominent stars within a few hundred light years from the Sun are candidates for becoming supernovae in as little as a millennium. One example is BetelgeuseBetelgeuse
Betelgeuse, also known by its Bayer designation Alpha Orionis , is the eighth brightest star in the night sky and second brightest star in the constellation of Orion, outshining its neighbour Rigel only rarely...
, a red supergiant
Red supergiant
Red supergiants are supergiant stars of spectral type K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive...
about 640 light-years from Earth. Though spectacular, these "predictable" supernovae are thought to have little potential to affect Earth.
Recent estimates predict that a Type II supernova would have to be closer than eight parsec
Parsec
The parsec is a unit of length used in astronomy. It is about 3.26 light-years, or just under 31 trillion kilometres ....
s (26 light-years) to destroy half of the Earth's ozone layer. Such estimates are mostly concerned with atmospheric modeling and considered only the known radiation flux from SN 1987A
SN 1987A
SN 1987A was a supernova in the outskirts of the Tarantula Nebula in the Large Magellanic Cloud, a nearby dwarf galaxy. It occurred approximately 51.4 kiloparsecs from Earth, approximately 168,000 light-years, close enough that it was visible to the naked eye. It could be seen from the Southern...
, a Type II supernova in the Large Magellanic Cloud
Large Magellanic Cloud
The Large Magellanic Cloud is a nearby irregular galaxy, and is a satellite of the Milky Way. At a distance of slightly less than 50 kiloparsecs , the LMC is the third closest galaxy to the Milky Way, with the Sagittarius Dwarf Spheroidal and Canis Major Dwarf Galaxy lying closer to the center...
. Estimates of the rate of supernova occurrence within 10 parsecs of the Earth vary from 0.05-0.5 per Ga to 10 per Ga. Several authors have based their estimates on the idea that supernovae are concentrated in the spiral arms of the galaxy, and that supernova explosions near the Sun usually occur during the ~10 million years that the Sun takes to pass through one of these regions (we are now in or entering the Orion arm
Orion Arm
The Orion–Cygnus Arm is a minor spiral arm of the Milky Way galaxy some 3,500 light years across and approximately 10,000 light years in length. The Solar System is within the Orion–Cygnus Arm...
). The relatively recent paper by Gehrels et al. uses a value of 3 supernovae less than 10 parsecs away per Ga. The frequency within a distance D is proportional to D3 for small values of D, but for larger values is proportional to D2 because of the finite thickness of the galactic disk (at intergalactic distances D3 is again appropriate). Examples of relatively near supernovae are the Vela Supernova Remnant
Vela Supernova Remnant
The Vela supernova remnant is a supernova remnant in the southern constellation Vela. Its source supernova exploded approximately 11,000-12,300 years ago...
(~800 ly, ~12,000 years ago) and Geminga
Geminga
Geminga is a neutron star approximately 250 parsecs away from the Sun in the constellation Gemini. Its name is both a contraction of "Gemini gamma-ray source", and gh'è minga "it's not there" in the Lombard dialect of Milan .- Pulsar :...
(~550 ly, ~300,000 years ago).
Type Ia supernovae are thought to be potentially the most dangerous if they occur close enough to the Earth. Because Type Ia supernovae arise from dim, common white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
stars, it is likely that a supernova that could affect the Earth will occur unpredictably and take place in a star system that is not well studied. One theory suggests that a Type Ia supernova would have to be closer than 10 parsecs (33 light-years) to affect the Earth. The closest known candidate is IK Pegasi. It is currently estimated, however, that by the time it could become a threat, its velocity in relation to the Solar System would have carried IK Pegasi to a safe distance.
Past events
Evidence from daughter products of short-lived radioactive isotopes shows that a nearby supernova helped determine the composition of the Solar SystemSolar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
4.5 billion years ago, and may even have triggered the formation of this system. Supernova production of heavy elements over astronomic periods of time ultimately made the chemistry of life
Biochemistry
Biochemistry, sometimes called biological chemistry, is the study of chemical processes in living organisms, including, but not limited to, living matter. Biochemistry governs all living organisms and living processes...
on Earth possible.
In 1996, astronomers at the University of Illinois at Urbana-Champaign
University of Illinois at Urbana-Champaign
The University of Illinois at Urbana–Champaign is a large public research-intensive university in the state of Illinois, United States. It is the flagship campus of the University of Illinois system...
theorized that traces of past supernovae might be detectable on Earth in the form of metal isotope signatures in rock strata. Subsequently, iron-60 enrichment has been reported in deep-sea rock of the Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
by researchers from the Technical University of Munich
Technical University of Munich
The Technische Universität München is a research university with campuses in Munich, Garching, and Weihenstephan...
. 23 atoms of this iron isotope were found in the top 2 cm of crust, and these date from the last 13 million years or so. It is estimated that the supernova must have occurred in the last 5 million years or else it would have had to have happened very close to the solar system to account for so much iron-60 still being here. A supernova occurring as close as would have been needed would have probably caused a mass extinction, which didn't happen in that time frame. The quantity of iron seems to indicate that the supernova was less than 30 parsecs away. On the other hand, the authors estimate the frequency of supernovae at a distance less than D (for reasonably small D) as around (D/10 pc
Parsec
The parsec is a unit of length used in astronomy. It is about 3.26 light-years, or just under 31 trillion kilometres ....
)3 per Ga, which gives a probability of only around 5% for a supernova within 30 pc in the last 5 million years. They point out that the probability may be higher because we are entering the Orion arm
Orion Arm
The Orion–Cygnus Arm is a minor spiral arm of the Milky Way galaxy some 3,500 light years across and approximately 10,000 light years in length. The Solar System is within the Orion–Cygnus Arm...
of the Milky Way.
Adrian L. Melott et al. estimated that gamma ray burst
Gamma ray burst
Gamma-ray bursts are flashes of gamma rays associated with extremely energetic explosions that have been observed in distant galaxies. They are the most luminous electromagnetic events known to occur in the universe. Bursts can last from ten milliseconds to several minutes, although a typical...
s from "dangerously close" supernova explosions occur two or more times per thousand million years, and this has been proposed as the cause of the end Ordovician extinction
Ordovician-Silurian extinction events
The Ordovician–Silurian extinction event, or quite commonly the Ordovician extinction, was the third-largest of the five major extinction events in Earth's history in terms of percentage of genera that went extinct and second largest overall in the overall loss of life. Between about 450 Ma to 440...
, which resulted in the death of nearly 60% of the oceanic life on Earth.
In 1998 a supernova remnant
Supernova remnant
A supernova remnant is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar material it sweeps up and shocks along the way.There are two...
, RX J0852.0-4622
RX J0852.0-4622
RX J0852.0-4622 is a recently discovered supernova remnant. The remnant is located in the southern sky in the constellation Vela , and sits inside the much larger and older Vela Supernova Remnant...
, was found in front (apparently) of the larger Vela Supernova Remnant
Vela Supernova Remnant
The Vela supernova remnant is a supernova remnant in the southern constellation Vela. Its source supernova exploded approximately 11,000-12,300 years ago...
. Gamma rays from the decay of titanium-44 (half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
about 60 years) were independently discovered coming from it, showing that it must have exploded fairly recently (perhaps around 1200 CE
Common Era
Common Era ,abbreviated as CE, is an alternative designation for the calendar era originally introduced by Dionysius Exiguus in the 6th century, traditionally identified with Anno Domini .Dates before the year 1 CE are indicated by the usage of BCE, short for Before the Common Era Common Era...
), but there is no historical record of it. The flux of gamma rays and x-rays indicates that the supernova was relatively close to us (perhaps 200 parsecs or 660 ly). If so, this is a surprising event because supernovae less than 200 parsecs away are estimated to occur less than once per 100,000 years.
In 2009, researchers have found nitrate
Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
s in ice core
Ice core
An ice core is a core sample that is typically removed from an ice sheet, most commonly from the polar ice caps of Antarctica, Greenland or from high mountain glaciers elsewhere. As the ice forms from the incremental build up of annual layers of snow, lower layers are older than upper, and an ice...
s from Antarctica at depths corresponding to the known supernovae of 1006 and 1054 CE, as well as from around 1060 CE. The nitrates were apparently formed from nitrogen oxides created by gamma rays from the supernovae. This technique should be able to detect supernovae going back several thousand years.