“Experts” had predicted the defunct Chinese space station would fall to Earth probably in the South Atlantic. Or maybe the South Pacific. Or perhaps some place else. So, plan accordingly. Ha-ha.

The dead satellite chose Sunday night North American time and the South Pacific not that far from Tahiti. Big splash. Chinese officials said its craft was unlikely to hit anyone. But if anyone saw debris, they should run away because it would likely be engine parts covered with toxic hydrazine.

The science of crashing satellites of the 8.5-ton variety is an inexact one. An unpredictable amount of a school-bus-sized object burns up at speeds around 17,000 miles an hour as it slashes into the thicker atmosphere from 65 miles down.

But such predictability is likely to be badly-needed information in the future as millions of foreign objects currently zoom around the planet. More are sent into orbit all the time.

China itself worsened the problem of space debris a few years ago by testing a satellite-killing missile on one of its own. It worked. But the Ka-Blam sent thousands of new pieces of debris into orbit, any one of which could take out communications and surveillance satellites or the International Space Station, which China has declined to be part of.

On average 200 to 400 man-made objects fall through the atmosphere every year. China and others had reassured the world’s 7.3 billion residents (about 1.4 billion of them Chinese) that they were probably safe, the world being pretty big and 70 percent of it covered by water. “No need for people to worry,” they said.

One woman in Russia was injured by space debris some years ago, but the odds of safety are even better than the odds of  being hit by lightning, they say.

China launched the crashed satellite in 2011. It was visited by two crews over time and shut down in 2013. But, oops, China lost control of it two years ago. So sorry. And along with U.S. space officials, it could only monitor its slow descent to flaming destruction ever since.

A lot of junk is floating around at high speeds up there from astronaut tools that escaped their grasp to spent rocket boosters. The European Space Agency estimates 170 million bits larger than a millimeter, 670,000 larger than a centimeter and 29,000 larger than 10 centimeters or four inches. The largest object to fall was Russia’s Mir Space Lab in 2001 at 120 tons. After a six-year orbit the 85-ton U.S. Skylab crashed in 1979.

The near earth orbit is seriously polluted with junk. The Air Force’s global Space Surveillance Network monitors all objects larger than a baseball, predicting orbital collisions so the 17,500 mile-an-hour International Space Station can often be adjusted to dodge pieces.

There are three, no, four kinds of earth satellites — those in low-Earth orbits like the football-field-sized Space Station at 250 miles altitude, medium-Earth satellites about 12,500 miles out, mainly for GPS use, and geostationary satellites like the ones that deliver TV to your roof-top dish. They’re about 22,500 miles out and parked to orbit at the same speed as Earth revolves so they hang over the same place.

Then, there are elliptical orbits with satellites flashing close to Earth and then heading out into space long distances as part of their loop. That’s what the first satellite was — Russia’s Sputnik I, dramatically launched on Oct. 4, 1957 when I was in study hall and the principal played its beeping signal on the school speakers. That meant America was behind.

Of course, the military and the U.S. National Reconnaissance Office have their own secret satellite networks, which can detect, for instance, truck traffic to North Korean missile test sites. But if we told you about them, we’d have to kill you.