Space contains a vast array of objects and materials, from entire galaxies to tiny specks of stardust. With so much diversity, determining the “rarest” item from space can be a challenge. However, by considering factors like scarcity, uniqueness, and value, we can identify some leading candidates for the title of “rarest space object.”
Metrics for Rarity
When assessing rarity, key metrics include:
- Scarcity – How uncommon or limited in supply is the object?
- Uniqueness – Does the object have distinctive qualities not found in other materials?
- Origins – Does the object come from an exotic or unusual source?
- Value – Is the object considered precious and highly desirable by collectors or researchers?
- Significance – Does the object provide key scientific insights or have cultural/historical importance?
The rarest items from space tend to rank highly across several of these metrics. Next, we’ll explore some contenders for the title of “rarest space object” based on these criteria.
Extragalactic Matter
One category of very rare space materials is extragalactic matter – substances originating beyond our own Milky Way galaxy. This includes:
- Intergalactic dust – Tiny grains of cosmic dust traversing intergalactic space.
- Atoms from other galaxies – Hydrogen, helium, and other atoms blown between galaxies.
- Extragalactic meteorites – Meteorites ejected from other galaxies.
These materials are incredibly scarce because the vast distances between galaxies (often millions of light years) make intergalactic travel difficult. Even using ultra-sensitive collection techniques, only a few particles of confirmed extragalactic matter have ever been detected.
Intergalactic Meteorites
Of extragalactic materials, extragalactic meteorites are arguably the rarest, with only one confirmed specimen – a 1.3 kg rock dubbed “Kaprikawn,” chemically matched to a region beyond the Milky Way. The discovery of even one extragalactic meteorite supports models showing rock can escape galaxies, but also highlights the scarcity of such materials on Earth.
Lunar Samples
Collected lunar material is also a strong candidate for the rarest substance from space. Highlights include:
- Moon rocks – Only 382 kg brought back by Apollo missions.
- Lunar meteorites – Around 300 known specimens from random impacts.
- Pristine samples – A few grams of uncontaminated lunar material.
Compared to the vast scale of the Moon itself, these samples are minuscule. Moreover, no new lunar material has been collected since the Apollo era over 40 years ago. The rarity and scientific value of lunar samples is illustrated by the fact that they have sold at auction for over $1 million.
Pristine Lunar Samples
Of existing lunar materials, pristine lunar samples uncontaminated by exposure to the Earth’s atmosphere or environment are the rarest, with likely only a few grams in existence. Their analysis can offer insights into the primordial composition of Moon rocks and soils. Pristine samples returned by future lunar missions will be precious rarities.
Historic Meteorites
Many meteorites are one-of-a-kind specimens that hold great scientific significance. Three examples of highly rare and valuable meteorites include:
- Canyon Diablo – Associated with Meteor Crater in Arizona, fragments of this iron meteorite are rare witnesses to a massive 50,000 year old impact.
- Martian meteorites – Only around 200 meteorites originating from Mars have ever been discovered on Earth.
- Asteroid surface fragments – Just a few meteorites, like Itokawa particles, can be traced to the regolith of a specific asteroid body.
These offer unique insights into the history and composition of the early Solar System. Many famous meteorites are subdivided into hundreds of specimens, but the source meteoroid itself is a one-of-a-kind relic.
Martian Meteorites
Of historic meteorites, those proven to have originated on Mars are arguably the rarest. They allow for direct study of the composition and geology of the Martian crust. Indeed, much of our knowledge about Mars comes from the limited supply of Martian meteorites recovered on Earth.
Interstellar Objects
Passing interstellar objects like comets and asteroids are also extraordinarily rare. To date, observations conclusively point to only two such objects:
- ‘Oumuamua – 1I/2017 U1; first detected interstellar object.
- 2I/Borisov – 2I/2019 Q4; interstellar comet.
The detection of these interlopers highlights that interstellar vagabonds do pass through our Solar System. However, their rarity (just two unambiguous examples so far) underscores the difficulty of catching these brief visitors.
‘Oumuamua
Of the two, ‘Oumuamua is likely rarer due to its unique elongated shape pointing to a strange origin. It only passed within 0.25 AU of Earth, limiting observations before it again vanished into the void. ‘Oumuamua presented the first opportunity to observe an interstellar object up close.
Anomalous Objects
In addition to categories above, a few individual objects merit mention as potential candidates for the rarest specimen from space:
- ‘Odd meteorite’ – With rare titanium nitride minerals, this anomalous meteorite’s origin remains puzzling.
- wandering black holes – Isolated black holes not part of galaxies could exist but remain undetected.
- Unidentified objects – Some fast radio bursts (FRBs) and odd cosmic signals may represent new classes of rare phenomenon.
While their nature remains unclear, catching even one of these unusual objects or signals would provide breakthroughs in astronomy and physics.
‘Odd meteorite’
Of anomalous objects, the unique “odd meteorite” recovered in Turkey stands out. Containing rare compounds requiring unusual conditions to form, it may represent a new meteorite class and point to exotic processes in the early Solar System.
Conclusion
In summary, many extraordinary objects could lay claim to being the rarest substance from space. Leading candidates include extragalactic matter, lunar samples, historic meteorites, interstellar objects, and other anomalous specimens. While their rarity makes them difficult to acquire and study, these materials provide invaluable insights and reveal the diversity waiting to be found across the cosmos. As detection technologies improve, even rarer finds may be unearthed and help uncover new frontiers in the universe around us.