It's impossible to give a single speed for "modern space probes" because they travel at vastly different speeds depending on their mission and destination. Here's a breakdown of the factors involved:

Factors Affecting Space Probe Speed:

* Mission: Probes designed to reach distant planets travel much faster than those orbiting nearby objects like the Moon.

* Launch Vehicle: More powerful rockets can launch probes at higher initial velocities.

* Gravity Assists: Using the gravity of planets to "slingshot" a probe can dramatically increase its speed.

* Destination: The further a probe travels, the more speed it needs to reach its destination within a reasonable timeframe.

Examples:

* Voyager 1 & 2: These probes hold the record for the fastest human-made objects, reaching speeds over 38,000 miles per hour (61,000 km/h) due to multiple gravity assists.

* New Horizons: This probe, which flew by Pluto, reached speeds over 36,000 miles per hour (58,000 km/h) after using a gravity assist from Jupiter.

* Parker Solar Probe: This probe is designed to fly close to the Sun and reaches speeds of 430,000 miles per hour (692,000 km/h) during its closest approaches.

* Mars Rovers: These probes travel at much slower speeds, typically around 5,000 miles per hour (8,000 km/h) due to their more complex trajectories and the need for a safe landing on Mars.

In Summary:

Modern space probes travel at a wide range of speeds, from a few thousand miles per hour to hundreds of thousands of miles per hour. The specific speed depends heavily on the mission, the launch vehicle, and the chosen trajectory.