Almost all the guesswork in the Solar System's total weight comes from one single, invisible spot in space.
March 19, 2026
Original Paper
Mass Inventory of the Solar System Beyond the Sun: A Systematic Compilation with Uncertainty Budget
arXiv · 2603.17561
The Takeaway
While we know the weights of the planets with extreme precision, the total mass of our solar system remains a surprisingly fuzzy estimate. Researchers found that 98.2% of that uncertainty is caused by the inner Oort Cloud—a massive, unobserved shell of icy debris that we have yet to see directly.
From the abstract
We compile a systematic mass inventory of the Solar System excluding the Sun, drawing on spacecraft measurements, planetary ephemerides, and population surveys of small-body populations including main-belt asteroids and trans-Neptunian objects. Using a Monte Carlo simulation with 100,000 realisations, and treating poorly constrained components (scattered disc, Oort cloud) as log-normal distributions, we obtain a total non-solar mass of 462 Earth masses (median), with a 68% credible interval of [