Time Jumper

The Time-Jumper is a Gateship capable of Time travel. It was built by an Ancient scientist named Janus by means of a device installed in the cargo hold. In the main timeline, this experimental technology was banned by the Atlantean Council in order to prevent dangers associated with time travel.

Purpose
It is unknown why Janus built the time ship. However, it is speculated he was experimenting with Time travel, perhaps attempting to perfect it as a means of traveling back in time in hope of ending or preventing the war with the Wraith.

Main Summary
In an alternate reality, members of the Atlantis Expedition discovered a special puddle jumper in Atlantis's jumper bay, one which was capable of time travel. In that reality, the expedition had suffered tragedy immediately upon arriving at the ancient city, because the shield had begun to fail from lack of power, causing the city to flood. Desperate and with no method of escape, the alternate versions of John Sheppard, Elizabeth Weir, and Radek Zelenka sealed themselves in this jumper as the jumper bay flooded. They subsequently activated the time device by accident.

They traveled 10,000 years into the past, arriving at the final days of the Ancients' war with the Wraith. Orbiting Wraith ships sieging Atlantis mistook the newly-arrived time jumper for a contemporary Atlantean craft, and opened fire, causing the jumper to crash land on Lantea. The alternate Sheppard and Zelenka were both killed in the crash, but the alternate Weir and the jumper itself were rescued by the Ancients inhabiting Atlantis, including Janus. Meeting a woman from 10,000 years in the future prompted the Atlantean Council's decision to ban further time-travel research, thus changing the timeline such that Janus's prototype would no longer be left behind for the expedition to later find. Fortunately, Janus ensured that the expedition would also be saved from drowning, in the new reality.

An identically-equipped puddle jumper, equally capable of time travel, was later discovered by SG-1 abandoned on a planet in the Milky Way galaxy. This newly discovered ship's time travel device was visually and functionally identical to the Janus prototype, implying that in the new timeline Janus chose to disobey the Atlantean Council's ban on time-travel research.

The time jumper was later discovered by SG-1 in Milky Way was most likely the new timeline's version of Janus's original prototype, which thanks to the intervention of alternate Weir, was evacuated through the Stargate to Milky Way instead of being left behind on Atlantis as it was in the previous timeline.

Alternatively, it is also possible that the pod discovered by SG-1 is the exact same pod which was originally flown back in time by the alternate Weir, left over as a temporal orphan. Since it reverted to Janus's possession following its crash-landing and recovery, he was actually in possession of both iterations of the pod when the Ancients evacuated the city. Therefore, it is plausible that this is actually the same ship, repaired. If this interpretation of events is correct, it would make the jumper more than 20,000 years old by the time it was finally discovered by SG-1.

This jumper was later used by SG-1 as a means of traveling back in time to ancient Egypt, in order to steal a ZPM from Ra, setting into motion the somewhat convoluted series of events depicted in Moebius, and further aging the time jumper by about five thousand years... twice.

Fate
It is unknown what has happened to this jumper as it is not seen, heard, nor mentioned of. It is assumed it was destroyed as mentioned by the alternate Samantha Carter in Moebius, Part 2 who like her "prime counterpart" believed it would be best if the time jumper be destroyed to prevent damaging the timeline any furthur. It is possible that the time jumper might have still been hidden elsewhere either on Earth or at another location.