Here's why:

* Melting point is the temperature at which a substance transitions from solid to liquid. This is determined by the internal structure and forces within the substance itself.

* Altitude primarily affects atmospheric pressure. While lower pressure at higher altitudes can influence the boiling point of water (making it boil at a lower temperature), it doesn't change the temperature at which water transitions from ice to liquid.

Therefore, the melting point of water at 5000 meters (or any altitude) remains at 0 degrees Celsius (32 degrees Fahrenheit).