Spatial Anomaly 521
A phenomenon which travels through subspace, occasionally moving into normal space for a time before returning. While in normal space subspace ellipses tend to sweep up various objects which are then carried along inside them. The ellipses can be billions of years old, and extremely ancient artefacts are sometimes discovered within them. The anomalies have only been encountered a handful of times; on October 19th, 2032, a subspace ellipse passing by Mars collided with and absorbed the Aries 4, one of the first manned spacecraft Mankind sent to the planet. This marked mankind's first encounter with a spatial anomaly, and almost derailed the Mars program entirely.
In 2376 USS Voyager encountered the same ellipse. The emergence of the phenomenon caused level 9 gravimetric distortions to emenate from subspace, and Voyager measured its total energy at 30 million Terajoules. The ellipse was strongly attracted towards Voyager, approaching at sufficient speed to prevent the starship from outrunning it at impulse and produced interference which disrupted the ships warp drive, making escape extremely difficult. The gravimetric stresses created are sufficient to rip the hull plating off a Starship, and no vessel which has passed close to a graviton ellipse has survived the encounter.9
Fortunately, Seven of Nine recognized the ellipse as Borg spatial anomaly 521 and recalled that it was attracted to objects which emit electromagnetic energy. She advised cutting power and reversing shield polarity, measures which prevented further pursuit and allowed Voyager to escape the anomaly.
Upon scanning the ellipses interior, Voyager detected a stable region within which gravimetric disturbances were negligible. The scans located some 2.8 billion compounds inside, including the hull materials of the Aries 4. Voyagers crew modified the shields of the Delta Flyer to allow it to penetrate the ellipse and discovered the space craft nearly intact within. Whilst the Flyer was within the ellipse the anomaly collided with a dark matter asteroid, badly damaging the shuttlecraft. Although this made retrieving the Aries impossible, they were able to recover the body of Lieutenant John Kelley from the capsule and give it a proper burial.9