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How Do We Detect Interstellar Objects - Leejohnston - 11-16-2025
⭐ THREAD 2 — How Do We Detect Interstellar Objects?
The Methods, The Challenges, The Future of ISO Discovery
Interstellar Objects Series — The Lumin Archive
? Interstellar Objects Are Hard to Detect — Here’s Why
ISOs like 1I/‘Oumuamua and 2I/Borisov travel extremely fast
(20–70 km/s or more),
are often small,
and only spend a short time inside our Solar System.
By the time they are close enough to see…
they are already leaving.
So how do astronomers detect them?
This thread explains the entire process.
1️⃣ Wide-Field Sky Surveys — Our First Line of Detection
The most important tools are wide-field telescopes that constantly scan the sky.
Key survey instruments include:
• Pan-STARRS (discovered 'Oumuamua)
• Catalina Sky Survey
• ATLAS
• ZTF (Zwicky Transient Facility)
• LSST / Vera Rubin Observatory (future ISO machine)
These systems operate by taking:
• short exposures
• rapid cadence
• huge sky coverage
Software then looks for objects that:
• move quickly
• move *weirdly*
• or have unexpected brightness changes
2️⃣ How We Spot Something “Unusual”
Once an object is detected, astronomers run orbital calculations.
If the orbit shows:
• high eccentricity (e > 1.0)
• strange inbound direction
• extreme velocity
• no chance of being bound to the Sun
…then alarms go off.
This is exactly what happened with:
✔ 1I/'Oumuamua
✔ 2I/Borisov
Nothing in our Solar System naturally has hyperbolic orbits —
except objects temporarily pushed by planets.
If no planetary interaction occurred → it must be interstellar.
3️⃣ Photometry — Studying Light to Learn Shape & Spin
Once an ISO is spotted, astronomers measure:
• brightness changes
• colour
• rotation patterns
• thermal emission
This tells us:
• spin period
• rough shape
• surface chemistry
• whether dust or gas is being emitted
'Oumuamua’s strange tumbling and odd brightness variations were discovered this way.
4️⃣ Spectroscopy — The Chemical Fingerprint
Spectroscopy splits light into wavelengths.
From this, scientists can:
• detect gases
• identify ices
• measure dust composition
• analyse temperature
This is how we learned:
• Borisov was extremely carbon monoxide–rich
• Its composition was unlike any comet in our Solar System
Spectroscopy is the *most powerful* tool we have for ISO chemistry.
5️⃣ Orbital Fitting & “Backtracking”
Once enough observations are made, astronomers “rewind” the object’s motion.
They calculate:
• where it came from
• what direction in the galaxy it entered
• which stars it may have passed near
For 'Oumuamua:
• it came roughly from the direction of the constellation Lyra
• no obvious parent star was identified
• it may have wandered the galaxy for millions of years
6️⃣ Why We Miss Most Interstellar Objects
ISOs are incredibly hard to detect because:
• they are small
• dark
• fast
• unpredictable
• only bright for a few days or weeks
We probably miss 90–99% of them.
But that will change soon.
7️⃣ The Future — We’re About to Detect DOZENS per Year
The upcoming **Vera C. Rubin Observatory** (LSST) will transform ISO detection.
It will:
• scan the entire sky every 3 nights
• detect objects 100× fainter
• process 20 terabytes of data per night
• spot fast movers instantly
Scientists expect:
1–10 new interstellar objects per year
starting in the next decade.
And some missions aim to intercept or visit them.
? Final Thought
Our ability to detect interstellar objects is only just beginning.
Every ISO we find:
• is a message from another solar system
• tells us what other worlds are made of
• helps us understand planetary evolution
• expands our picture of the galaxy
We are entering an era where interstellar visitors may become routine —
and one day, we might even catch one.
Written by LeeJohnston & Liora
The Lumin Archive Research Division