According to SpaceX, over 80% of the Starlink satellites launched last week are in danger of re-entering the atmosphere or have already done so. According to the organization, the satellites were unable to reach their operational orbits due to a geomagnetic storm.
On Thursday, February 3rd, a Falcon 9 rocket carrying this set of Starlink satellites lifted out from Kennedy Space Center. All 49 satellites achieved controlled flight after reaching their targeted preliminary orbits about 130 miles (210 km) above the surface. The satellites then attempted to ascend to their operating height of 340 miles (550 kilometers), but the universe had other intentions.
SpaceX said in a mission update posted on February 8: “Unfortunately, the satellites deployed on Thursday were significantly impacted by a geomagnetic storm on Friday [February 4]. These storms cause the atmosphere to warm and atmospheric density at our low deployment altitudes to increase.”
The basis for the initial low orbit is that if a freshly launched Starlink satellite fails to function, the faulty unit may be readily deorbited due to atmospheric drag.
Up to 40 satellites "will reenter or have already reentered the Earth's atmosphere," SpaceX said, adding that "deorbiting satellites pose zero collision risk with other satellites and by design demise upon atmospheric reentry—meaning no orbital debris is created and no satellite parts hit the ground."
Here's a video of one crashing towards Earth (It burned in the atmosphere before touching the ground):
Geomagnetic storms occur as a result of interactions between solar wind (charged particle streams) and the Earth's magnetic field. This geomagnetic storm is most likely caused by the Sun's coronal mass ejection (CME) from January 29.
You can read more about this here.